AbstractWhen a drug candidate—i.e., a new chemical entity (NCE) or new molecular entity (NME)—is discovered, there is a requirement to identify a vehicle for in vitro and/or in vivo evaluation to assess the activity and/or toxicity of the compound (here we refer to the biologically active compound as the active pharmaceutical ingredient: API). Ideally, this vehicle will not impart any biological activity or any toxicity that would mask or confound the effects of the API. At this early stage in development, and given the high attrition rates of drug candidates in discovery, it does not make sense to fully characterize the API—speed and cost are generally the driving factors. This chapter provides guidance for the development of early‐stage test articles (i.e., drug products containing APIs intended to be used for the in vitro and/or in vivo evaluation) and not necessarily formulations that are intended to progress into clinical evaluation. © 2017 by John Wiley & Sons, Inc.