Fractionation, in the most general sense, could mean any process whereby a mixture is separated into different components or fractions. Fractionation in this general sense, however, would include diverse methods and techniques that may have little in common. Such methods and techniques may be broadly grouped in four classes, namely fractionation proper, general separation, analytical separation and purification. It is important to note, however, that this is not an exclusive classification as some methods may have characteristics belonging to more than one of these classes. Fractionation proper in the restricted commonly accepted sense, sometimes referred to as thermal separation, may be defined as any physical fractional or separation process involving a phase transition in which a mixture is separated in a single run into two or more fractions with variable compositions. The mixture to be separated could be a homogeneous mixture such as a solution or a heterogeneous mixture such as a mixture of solid and liquid. The mixture to be separated may also be gaseous, liquid or solid. The fractions are separated based on differences in a specific property of the individual components such as boiling, freezing or melting points. The phase changes involved could be condensation for vapours and gases (dephlegmation), boiling and evaporation (distillation) or freezing and crystallisation (freeze distillation and solution crystallisation) for liquids, and melting or sublimation for solids. Most of these processes find application on industrial scales but some processes such as fractionation by sublimation are restricted to laboratory-scale procedures.