diff --git a/docs/src/manual/users.md b/docs/src/manual/users.md
index b5d51f0..c094e44 100644
--- a/docs/src/manual/users.md
+++ b/docs/src/manual/users.md
@@ -44,8 +44,13 @@ AuChimiste.Composition
 
 ## Interfaces
 
+The following interfaces are provided as a centralization of names for the package. Generally these functions will take an object with the type for which they implement the quantity associated with their name, and other relevant parameters, such as temperature, pressure, and/or an array of mass fractions. In all cases values are expected to be returned in SI units, as documented by each function.
+
 ```@docs
+AuChimiste.density
 AuChimiste.specific_heat
+AuChimiste.enthalpy
+AuChimiste.entropy
 AuChimiste.thermal_conductivity
 AuChimiste.viscosity
 ```
diff --git a/src/interfaces.jl b/src/interfaces.jl
index f0f5226..aeb02fa 100644
--- a/src/interfaces.jl
+++ b/src/interfaces.jl
@@ -1,34 +1,49 @@
 # -*- coding: utf-8 -*-
 
+"""
+    density(args...; kwargs...)
+
+Evaluation of the density of a substance.
+Its return value must be in ``kg\\cdotp{}m^{-3}``.
+"""
+function density end
+
 """
     specific_heat(args...; kwargs...)
 
-Common interface for evaluation of the specific heat of a substance.
-Generally this function will take an object with the type for which it
-implements the specific heat, a temperature, and maybe an array of
-mass fractions. Its return value must be provided in standard SI units
-of ``J\\cdotp{}kg^{-1}\\cdotp{}K^{-1}``.
+Evaluation of the specific heat of a substance.
+Its return value must be in ``J\\cdotp{}kg^{-1}\\cdotp{}K^{-1}``.
 """
 function specific_heat end
 
+"""
+    enthalpy(args...; kwargs...)
+
+Evaluation of the enthalpy of a substance.
+Its return value must be in ``J\\cdotp{}kg^{-1}``.
+"""
+function enthalpy end
+
+"""
+    entropy(args...; kwargs...)
+
+Evaluation of the entropy of a substance.
+Its return value must be in ``J\\cdotp{}K^{-1}``.
+"""
+function entropy end
+
 """
     thermal_conductivity(args...; kwargs...)
 
-Common interface for evaluation of the thermal conductivity of a
-substance. Generally this function will take an object with the type
-for which it implements the thermal conductivity, a temperature, and
-maybe an array of mass fractions. Its return value must be provided
-in standard SI units of ``W\\cdotp{}m^{-1}\\cdotp{}K^{-1}``.
+Evaluation of the thermal conductivity of a substance.
+Its return value must be in ``W\\cdotp{}m^{-1}\\cdotp{}K^{-1}``.
 """
 function thermal_conductivity end
 
 """
     viscosity(args...; kwargs...)
 
-Common interface for evaluation of the viscosity of a substance.
-Generally this function will take an object with the type for which it
-implements the viscosity, a temperature, and maybe an array of mass
-fractions. Its return value must be provided in standard SI units of
-``Pa\\cdotp{}s``.
+Evaluation of the viscosity of a substance.
+Its return value must be in ``Pa\\cdotp{}s``.
 """
 function viscosity end