This chapter introduces bioactivity and bioaffinity terms in relation to mixture profiling and gives the significance of bioactivity and/or bioaffinity profiling of biologically active mixtures in general, and for bioactive mixtures in drug discovery research in particular. Further, the chapter gives an overview of the common and less common analytical approaches for bioactivity profiling of bioactive mixtures. Special focus is put on bioassay-guided fractionation as the standard technique employed (in identification and purification of bioactive molecules from a bioactive mixture), and on state-of-the-art post-column bioactivity profiling approaches, also providing examples and limitations of these analytical methods. On-column and pre-column bioactivity profiling analytics is also discussed. Examples of bioactive molecules identified and purified from different natural products are given with emphasis on molecules isolated from animal venoms. Finally, this chapter briefly discusses the importance of bioactivity profiling of metabolic mixtures in drug discovery.