When a biological drug patent expires, alternative biosimilar products are developed. Biological drugs are different in many respects from drugs based on chemically synthesized small molecules. The development of biosimilar products is complicated and involves numerous considerations and steps. The assessment of biosimilarity and interchangeability is complicated and difficult. This book presents current issues for the development of biosimilars and gives detailed reviews of its various stages and contributing factors as well as relevant regulatory pathways and post-approval issues.