Unlike the more common small-molecule drugs, biologics generally exhibit high molecular complexity, and may be quite sensitive to changes in manufacturing processes. Follow-on manufacturers do not have access to the originator’s molecular clone and original cell bank, nor to the exact fermentation and purification process, nor to the active drug substance. They do have access to the commercialized innovator product. Various factors, such as safety, pricing, manufacturing, entry barriers, physician acceptance, and marketing, will make the biosimilar market develop different from the generic market. The high cost to enter the market and the size of the biologic drug market make entry attractive but risky.