The main drawback of biotechnology-derived medicinal products is possibly their high price, which is posing a challenge for the sustainability of health care systems. The legislation on similar biological medicinal products has the same goal—that is, to try to reduce the cost of clinical treatments based on biological and biotech drugs by introducing market competition. This chapter discusses some of the initial challenges for their introduction that still remain Guidelines for biosimilar development were first published in 2005 and have been updated according to the experience gained. The main concepts in these guidelines and rationale are also described. In the EU, the regulatory framework for the development of biosimilar medicinal products is well established and provides relatively clear recommendations in terms of quality, nonclinical, and clinical criteria for their development. Biosimilars are being established as a good tool to reduce health care expenditure in the use of expensive biologics for many chronic indications.