Patents for biologic agents first marketed in the 1980s are now beginning to expire, opening the door for 'non-proprietary' versions of these agents to enter the market. However, there are fundamental differences between biologics and traditional pharmaceuticals that preclude the extrapolation of existing regulatory processes for traditional generic agents to these new biologic products. These include differences in dimensions (molecular weight), synthesis, purification, stability, and immunogenicity. There is also controversy over the terminology of these biologic agents, with a number of terms put forward. European regulatory authorities have adopted the term 'biosimilars,' while the US FDA prefers the term 'follow-on biologics.' It is important that these terms are not used as synonyms for 'generics,' and already there are moves to prevent classification of these products as 'generics.' In this review, we focus on the differences that exist between generics and biosimilars, and assess the current scenario of problems and opportunities. Furthermore, we also attempt to highlight the problems with establishing regulatory guidelines and those associated with the introduction of these drugs into clinical practice.