The first aim of this chapter is to describe the main representatives of substructure approaches and whole molecule approaches for logP calculation, to highlight their characteristics and to discuss their advantages and disadvantages. A further goal is a classification of currently available logP programs according to their methodological background. The limited reliability of logP programs urgently favours the use of a diverse set of programs instead of a single procedure. The majority of drugs is ionized at pH 7.4. Distribution coefficients (logD) reflect the lipophilicity of ionizable compounds; the implication of logD in drug development and available logD software are discussed. LogP and logD are of prime importance in ADMET predictions; a few examples for protein binding, BBB permeability, metabolism, and toxicity are given.