The number and diversity of biotherapeutic modalities continues to increase. These represent complex modalities such as peptide and peptide conjugates, antisense oligonucleotides, DNA- and RNA-based therapies, drug conjugates, as well as viral vector-based therapeutics. Biological assays are critical tools for drug discovery, development and analytical control strategies for biotherapeutics. The ability of these biological assays to reflect the relevant biological activities is essential; however, developing such assays is increasingly challenging given that these newer biotherapeutics possess a diversity of mechanism(s) of action. The session will focus on biological assays used for release and/or characterization of these emerging modalities, and the challenges to develop such assays. Talks will assess bioassay strategies, approaches and lessons learned.