diff --git a/doc/handbook/dumux-handbook.tex b/doc/handbook/dumux-handbook.tex
index 3904c88bd..9a956a60e 100644
--- a/doc/handbook/dumux-handbook.tex
+++ b/doc/handbook/dumux-handbook.tex
@@ -61,6 +61,10 @@
 
 \newcommand{\Dune}{{DUNE}\xspace}
 \newcommand{\Dumux}{DuMu$^\text{x}$\xspace}
+
+\newcommand{\porosity}{\phi}
+\newcommand{\saturation}{S}
+
 \newcommand{\doxyref}[3]{\textnormal{#1}}
 \newenvironment{CompactList}
 {\begin{list}{}{
@@ -146,6 +150,7 @@ Universit\"at Stuttgart, Paffenwaldring 61, D-70569 Stuttgart, Germany}\\
 \input{structure}
 \input{designpatterns}
 \input{propertysystem}
+\input{fluidframework}
 \input{models}
 \input{DumuxFlow}
 \input{NewtonInANutshell}
diff --git a/doc/handbook/fluidframework.tex b/doc/handbook/fluidframework.tex
index 835783c35..9cbfaf481 100644
--- a/doc/handbook/fluidframework.tex
+++ b/doc/handbook/fluidframework.tex
@@ -10,10 +10,355 @@ the concepts is given, then a few implementation details follow.
 
 \section{Overview of the Fluid Framework}
 
-The fundamental concepts of the \Dumux fluid framwork are fluid
-systems and fluid states. Fluid states are responsible for expressing
-the complete thermodynamic configuration of a system, while fluid
-systems are state-less classes which provide the relations that 
+The \Dumux fluid framework currently featurs the following concepts
+(listed roughly in their order of importance):
+
+\begin{description}
+\item[Fluid state:] Fluid states are responsible for representing the
+  complete thermodynamic configuration of a system. A fluid state
+  always provides access methods to {\bf all} thermodynamic
+  quantities, but the concept of a does not mandate what assumptions
+  are made to store these thermodynamic quantities. What fluid states
+  do {\bf not} do is to make sure that the thermodynamic state which
+  they represent is physically possible.
+\item[Fluid system:] Fluid systems express the thermodynamic {\bf
+    relations}\footnote{Strictly speaking, these relations are
+    functions, mathematically.} between quantities. Since functions do
+  not exhibit any internal state, all fluid systems are state-less
+  classes, i.e. all member functions are \texttt{static}. The
+  thermodynamic state is captured by a fluid state!
+\item[Parameter cache:] Since fluid systems sometimes require
+  computationally expensive parameters for multiple relations, these
+  parameters can be cached using a so-called parameter
+  cache. Parameter cache objects are specfic for each fluid system but
+  they must provide a common interface to specify which quantities
+  changed since the last invocation.
+\item[Constraint solver:] Constraint solvers are auxiliary tools to
+  make sure that a fluid state adheres to some thermodynamic
+  constraints. All constraint solvers specify a well defined set of
+  input variables make sure that the resulting fluid state is
+  consistent with a set of well-defined thermodynamic equations. See
+  section \ref{sec:constraint_solvers} for a detailed description of
+  the constraint solvers which are currently available in \Dumux.
+\item[Equation of state:] Equations of state (EOS) are auxiliary
+  classes which provide relations between a fluid phase's temperature,
+  pressure and density. Since these classes are only used internally
+  in the fluid systems, the classes for a EOS are ad-hoc and there is
+  currently no common interface for them.
+\item[Component:] Components are fluid systems which provide the
+  thermodynamic relations for the liquid and gas phase of a single
+  chemical species or a fixed mixture of species. Their main purpose
+  is to provide a convenient way to access these quantities from
+  full-fledged fluid systems, but they are not supposed to be used by
+  models directly.
+\item[Binary coefficient:] Binary coefficients express the relations
+  of a mixture of two components. Typical binary coefficients are
+  \textsc{Henry} coefficients or binary molecular diffusion
+  coefficients. So far, the programming interface for accessing binary
+  coefficients has not been standardized.
+\end{description}
+
+\section{Fluid States}
+
+{\bf All} fluid states {\bf must} export the following constants:
+\begin{description}
+\item[\texttt{numPhases}:] The number of fluid phases considered.
+\item[\texttt{numComponents}:] The number of considered chemical
+  species or pseudo-species.
+\end{description}
+
+Also, {\bf all} fluid states {\bf must} provide the following methods:
+\begin{description}
+\item[\texttt{temperature()}:] The absolute temperature $T_\alpha$ of
+  a fluid phase $\alpha$.
+\item[\texttt{pressure()}:] The absolute pressure $p_\alpha$ of a
+  fluid phase $\alpha$.
+\item[\texttt{saturation()}:] The saturation $S_\alpha$ of a fluid 
+  phase $\alpha$. The saturation is defined as the pore space occupied by the
+  fluid divided by the total pore space:
+  \[
+  \saturation_\alpha := \frac{\porosity \mathcal{V}_\alpha}{\porosity \mathcal{V}}
+  \]
+\item[\texttt{moleFraction()}:] Returns the molar fraction
+  $x^\kappa_\alpha$ of a component $\kappa$ in a fluid phase
+  $\alpha$. The molar fraction $x^\kappa_\alpha$ is defined as the number
+  of molecules of a component in a mixture divided by the total number
+  of molecules in the fluid.
+\item[\texttt{moleFraction()}:] Returns the mass fraction
+  $X^\kappa_\alpha$ of a component $\kappa$ in a fluid phase
+  $\alpha$. The mass fraction $X^\kappa_\alpha$ is defined as the
+  weight of a component in a mixture divided by the total mass of the
+  fluid. It is related with the component's mole fraction by means of
+  the relation
+  \[
+  X^\kappa_\alpha = x^\kappa_\alpha \frac{M^\kappa}{\overline M_\alpha}\;,
+  \]
+  where $M^\kappa$ is the molar mass of component $\kappa$ and
+  $\overline M_\alpha$ is the mean molar mass of a molecule of phase
+  $\alpha$.
+\item[\texttt{averageMolarMass()}:] Returns $\overline M_\alpha$, the
+  mean molar mass of a molecule of phase $\alpha$. For a mixure of $N
+  > 0$ components, $\overline M_\alpha$ is defined as
+  \[
+  \overline M_\alpha = \sum_{\kappa=1}^{N} x^\kappa_\alpha M^\kappa
+  \]
+\item[\texttt{density()}:] Returns the density $\rho_\alpha$ of a
+  fluid phase $\alpha$.
+\item[\texttt{molarDensity()}:] Returns the molar density
+  $\rho_{mol,\alpha}$ of a fluid phase $\alpha$. The molar density can
+  be defined using the mass density $\rho_\alpha$ and the mean molar mass $\overline M_\alpha$ by
+  \[
+  \rho_{mol,\alpha} = \frac{\rho_\alpha}{\overline M_\alpha} \;.
+  \]
+\item[\texttt{molarVolume()}:] Returns the molar volume
+  $V_{mol,\alpha}$ of a fluid phase $\alpha$. This quantity is just
+  the inverse of the molar density.
+\item[\texttt{molarity()}:] Returns the molar concentration
+  $c^\kappa_\alpha$ of component $\kappa$ in fluid
+  phase $\alpha$.
+\item[\texttt{fugacity()}:] Returns the fugacity $f^\kappa_\alpha$ of
+  component $\kappa$ in fluid phase $\alpha$. The fugacity is defined
+  as
+  \[
+  f_\alpha^\kappa := \Phi^\kappa_\alpha x^\kappa_\alpha p_\alpha \;,
+  \]
+  where $\Phi^\kappa_\alpha$ is the {\em fugacity coefficient}. The
+  physical meaning of fugacity becomes clear from the equation
+  \[
+  f_\alpha^\kappa = p_\alpha \exp\left\{\frac{\zeta^\kappa_\alpha}{R T_\alpha} \right\} \;,
+  % TODO: cite
+  \]
+  where $\zeta^\kappa_\alpha$ represents the $\kappa$'s chemical
+  potential in phase $\alpha$, $R$ stands for the
+  ideal gas constant, and $T_\alpha$ for the absolute
+  temperature phase $\alpha$. Assuming thermal equilibrium, there is a
+  one-to-one mapping between a component's chemical potential
+  $\zeta^\kappa_\alpha$ and its fugacity $f^\kappa_\alpha$. In this
+  case chemical equilibrium can thus be expressed by
+  \[
+  f^\kappa = f^\kappa_\alpha = f^\kappa_\beta \forall \alpha, \beta
+  \]
+\item[\texttt{fugacityCoefficient()}:] Returns the fugacity coefficient $\Phi^\kappa_\alpha$ of
+  component $\kappa$ in fluid phase $\alpha$.
+\item[\texttt{enthalpy()}:] Returns specific enthalpy $h_\alpha$ of a
+  fluid phase $\alpha$. 
+\item[\texttt{internalEnergy()}:] Returns specific internal energy $u_\alpha$ of a
+  fluid phase $\alpha$. The specific internal energy is defined by the relation
+  \[
+  u_\alpha = h_\alpha - \frac{p_\alpha}{\rho_\alpha}
+  \]
+\item[\texttt{viscosity()}:] Returns the dynamic viscosity
+  $\mu_\alpha$ of fluid phase $\alpha$.
+\end{description}
+  
+Currently, the following fluid states are available in \Dumux:
+\begin{description}
+\item[\texttt{NonEquilibriumFluidState}:] This is the most general
+  fluid state supplied. It does not assume thermodynamic equilibrium
+  and this stores all phase compositions (using mole fractions) and
+  fugacity coefficients, as well as all phase temperatures, pressures,
+  saturations and enthalpies.
+\item[\texttt{CompositionalFluidState}:] The
+  \texttt{NonEquilibriumFluidState} with the difference
+  \texttt{CompositionalFluidState} is similar to the difference that
+  is assumes thermodynamic equilibrium. In the context of multi-phase
+  flow in porous media, this means that only a single temperature
+  needs to be stored.
+\item[\texttt{ImmisicibleFluidState}:] This fluid state assumes that
+  the fluid phases are immiscible, which implies that the phase
+  compositions and the fugacity coefficients do not need to be stored
+  explicitly.
+\item[\texttt{PressureOverlayFluidState}:] This is a so-called {\em
+    overlay} fluid state. It allows to set the pressure of all fluid
+  phases but forwards everything else to an other fluid state.
+\item[\texttt{SaturationOverlayFluidState}:] This fluid state is like
+  the \texttt{PressureOverlayFluidState}, except that the phase
+  saturations are settable instead of the phase pressures.
+\item[\texttt{TempeatureOverlayFluidState}:] This fluid state is like
+  the \texttt{PressureOverlayFluidState}, except that the temperature
+  is settable instead of the phase pressures. Note that this overlay
+  state assumes thermal equilibrium regardless of underlying fluid
+  state.
+\item[\texttt{CompositionOverlayFluidState}:] This fluid state is like
+  the \texttt{PressureOverlayFluidState}, except that the phase
+  composition is settable (in terms of mole fractions) instead of the
+  phase pressures.
+\end{description}
+
+\section{Fluid Systems}
+
+\subsection{Parameter Caches}
+
+All fluid systems must export a type for their \texttt{Parameter}
+cache objects. For fluid systems which do not require to cache
+parameters, \Dumux provides a \texttt{NullParameterCache} class.
+
+Parameter caches must at least provide the following methods
+\begin{description}
+\item[updateAll(fluidState, except):] Update all cached quantities in
+  all phases. The \texttt{except} argument contains a bitfield of the
+  quantities which have not changed since the last call to a
+  \texttt{update()} method.
+  \item[updateAllPresures(fluidState):]
+    Update all cached quantities which depend on pressure for
+    all phases.
+  \item[updateAllTemperatures(fluidState):]
+    Update all cached quantities which depend on temperature for
+    all phases.
+  \item[updatePhase(fluidState, phaseIdx, except):] Update all cached
+    quantities for a given phase. The quantities specified by the
+    \texttt{except} bitfield have not been modified since the last
+    call to an \texttt{update()} method.
+  \item[updateTemperature(fluidState, phaseIdx):] Update all cached
+    quantities which depend on the temperature of a given phase.
+  \item[updatePressure(fluidState, phaseIdx):] Update all cached
+    quantities which depend on the pressure of a given phase.
+  \item[updateComposition(fluidState, phaseIdx):] Update all cached
+    quantities which depend on the composition of a given phase.
+  \item[updateSingleMoleFraction(fluidState, phaseIdx, compIdx):]
+    Update all cached quantities which depend on the value of a mole
+    fraction of a given components of a given phase.
+\end{description}
+Note, that the parameter cache interface only guarantees that if a
+more specialized \texttt{update()} method is called, it is not slower
+than the next more-general method (e.g. calling
+\texttt{updateSingleMoleFraction()} can be as expensive as
+\texttt{updateAll()}). It is thus advisable to rather use a broader
+\texttt{update()} method than more than one calls to specialized
+\texttt{update()} methods.
+
+To make usage of parameter caches easier for the case where all cached
+quantities ought to be re-calculated if the respective phase was
+changed, it is possible to just define the \texttt{updatePhase()} and
+derive a parameter cache from \texttt{Dumux::ParameterCacheBase}.
+
+\subsection{Exported Constants and Capabilities}
+
+Besides providing the type of their \texttt{ParameterCache} objects,
+fluid systems need to export the following constants:
+\begin{description}
+\item[\texttt{numPhases}:] The number of considered fluid phases.
+\item[\texttt{numComponents}:] The number of considered chemical (pseudo-) species.
+\item[\texttt{phaseName()}:] Given the index of a fluid phase, return a
+  human-readable string as its name.
+\item[\texttt{componentName()}:] Given the index of a component,
+  return a human-readable string as its name.
+\item[\texttt{isLiquid()}:] Return whether the phase is a liquid, given the index of a phase.
+\item[\texttt{isIdealMixture()}:] Return whether the phase is an ideal
+  mixture, given the index of a phase. In the context of the \Dumux
+  fluid framework a phase $\alpha$ is an ideal mixture if, and only if
+  all its fugacity coefficients $\Phi^\kappa_\alpha$ do not depend on
+  the phase composition. (Although they might very well depend on
+  temperature and pressure.)
+\item[\texttt{isIdealGas()}:] Return whether a phase $\alpha$ is an ideal
+  gas, i.e. it adheres to the relation
+  \[
+  p_\alpha V_{mol,\alpha} = R T_\alpha \;,
+  \]
+  with $R$ being the ideal gas constant.
+\item[\texttt{isCompressible()}:] Return whether a phase $\alpha$ is
+  compressible, i.e. its density depends on pressure $p_\alpha$.
+\item[\texttt{molarMass()}:] Given a component index, return the molar
+  mass of the corresponding component.
+\end{description}
+
+\subsection{Thermodynamic Relations}
+
+Fluid systems have been explicitly designed to provide as few
+thermodynamic relations as possible. A full-fledged fluid system thus
+only needs to provide the following methods:
+\begin{description}
+\item[\texttt{init()}:] Initialize the fluid system. This is usually
+  used tabulated to tabulate some quantites
+\item[\texttt{density()}:] Given a fluid state, an up-to-date parameter
+  cache and a phase index, return the density of the phase.
+\item[\texttt{fugacityCoefficient}:] Given a fluid state, an up-to-date
+  parameter cache as well as a phase and a component index, return the
+  fugacity coefficient of a the component for the phase.
+\item[\texttt{viscosity()}:] Given a fluid state, an up-to-date parameter
+  cache and a phase index, return the dynamic viscosity of the phase.
+\item[\texttt{diffusionCoefficient}:] Given a fluid state, an
+  up-to-date parameter cache and a phase index, return the dynamic
+  viscosity of the phase, calculate the molecular diffusion
+  coefficient for a component in a fluid phase
+  
+  Molecular diffusion of a component $\kappa$ in phase $\alpha$ is
+  caused by a gradient of the chemical potential and follows the law
+  \[ 
+  J^\kappa_\alpha = - D\ \mathbf{grad} \zeta^\kappa_\alpha\;,
+  \] 
+  where $\zeta^\kappa_\alpha$ is the component's chemical potential,
+  $D$ is the diffusion coefficient and $J^\kappa_\alpha$ is the
+  diffusive flux. $\zeta^\kappa_\alpha$ is connected to the
+  component's fugacity $f^\kappa_\alpha$ by the relation
+  \[ 
+  \zeta^\kappa_\alpha = 
+  R T_\alpha \mathrm{ln} \frac{f^\kappa_\alpha}{p_\alpha} \;.
+  \]
+\item[\texttt{binaryDiffusionCoefficient}:] Given a fluid state, an
+  up-to-date parameter cache, a phase index and two
+  component indices return the binary diffusion coefficient for
+  components for the binary mixture. This method is less general than
+  \texttt{diffusionCoefficient} method, but usually only binary
+  diffusion coefficients can be found in the literature.
+\item[\texttt{enthalpy}:] Given a fluid state, an up-to-date parameter
+  cache and a phase index, this method represents the specific
+  enthalpy $h_\alpha$ of the phase.
+\item[\texttt{thermalConductivity}:] Given a fluid state, an
+  up-to-date parameter cache and a phase index, this method represents
+  the thermal conductivity of the fluid phase.
+\item[\texttt{heatCapacity}:] Given a fluid state, an up-to-date
+  parameter cache and a phase index, this method represents the
+  isobaric heat capacity $c_{p,\alpha}$ of the fluid phase. The
+  isobaric heat capacity is defined as the partial derivative of the
+  specific enthalpy $h_\alpha$ to the fluid pressure:
+  \[
+  c_{p,\alpha} = \frac{\partial h_\alpha}{\partial p_\alpha}
+  \]
+\end{description}
+
+Fluid systems may chose not to implement some of these methods and
+throw a \texttt{Dune::NotImplemented} exception instead. Obviously,
+such fluid systems cannot be used in conjunction with models that
+depend on those methods.
+
+\subsection{Available Fluid Systems}
+Currently, the following fluid states are available in \Dumux:
+\begin{description}
+\item[\texttt{Dumux::FluidSystems::TwoPImmiscible}:] A two-phase fluid
+  system featuring which assumes immiscibility of the fluid
+  phases. The fluid phases are thus specified by means of their
+  constituting components. This fluid system is intented to be used
+  with models that assume immiscibility.
+\item[\texttt{Dumux::FluidSystems::H2ON2}:] A two-phase fluid system
+  featuring the gas and liquid phases and destilled water ($H_2O$) and
+  pure molecular Nitrogen ($N_2$) as components.
+\item[\texttt{Dumux::FluidSystems::H2OAir}:] A two-phase fluid system
+  featuring the gas and liquid phases and destilled water ($H_2O$) and
+  air (Pseudo component composed of $79\%\;N_2$, $20\%\;O_2$ and
+  $1\%\;Ar$) as components.
+\item[\texttt{Dumux::FluidSystems::H2OAirMesitylene}:] A three-phase fluid
+  system featuring the gas, NAPL and water phases and destilled water
+  ($H_2O$) and air and Mesitylene ($C_6H_3(CH_3)_3$) as components. This fluid
+  system assumes all phases to be ideal mixtures.
+\item[\texttt{Dumux::FluidSystems::H2OAirXylene}:] A three-phase fluid
+  system featuring the gas, NAPL and water phases and destilled water
+  ($H_2O$) and air and Xylene ($C_8H_{10}$) as components. This fluid
+  system assumes all phases to be ideal mixtures.
+\item[\texttt{Dumux::FluidSystems::Spe5}:] A three-phase fluid system
+  featuring the gas, oil and water as phases and the seven components
+  distilled water ($H_2O$), Methane ($C_1$), Propane ($C_3$), Pentane
+  ($C_5$), Heptane ($C_7$), Decane ($C_{10}$), Pentadecane
+  ($C_{15}$) and Icosane ($C_{20}$). For the water phase the IAPWS-97
+  formulation is used as equation of state, while for the gas and oil
+  phases a \textsc{Peng}-\textsc{Robinson} equation of state with
+  slightly modified parameters is used. This fluid system is highly
+  non-linear, and the gas and oil phases can also not be considered as
+  ideal mixtures. % TODO: citation
+\end{description}
+
+\section{Constraint Solvers}
+\label{sec:constraint_solvers}
 
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