With recent FDA approval of biosimilars in the US emphasis on accurate and robust characterization is paramount. Regulations and guidelines (FDA and ICH) regarding what constitutes appropriate characterization include primary sequence analysis, secondary and tertiary structure analysis, and immnuohistochemical responses. This seminar highlights the current spectroscopic and biophysical methods that can be used to characterize biosimilars and biologics during the initial process development stage. These methods can also be applied to assay changes, if any, in the final drug product.