The prime difference between generics and biosimilars is that while generics contain the exact active ingredient as in the originator product, biosimilars are only “similar” and not “identical” to the originator biological medicine. This difference appears due to the nature of the biopharmaceutical medicines which are extremely complex to manufacture (it is not possible to make an exact copy of a biotech medicine in the same way as a traditional chemical molecule can be copied). In fact, it is widely accepted that for biopharmaceuticals, the “process is the product”. Minor changes during the manufacturing process can have critical consequences in the patients. The vast majority of the biopharmaceuticals on the market are produced by genetic engineering using various recombinant expression systems. Most of the recombinant proteins that have been granted marketing approval to date are produced either in E. Coli or in recombinant mammalian cell lines. Several approaches may be undertaken to determine biopharmaceuticals potency. Bioassays represent the most relevant potency-determining assay, as they directly assess the biological activity of the product. These assays involve applying a known quantity of the substance to be analyzed to a biological system which responds to this applied stimulus. The response is measured quantitatively, allowing an activity value to be assigned to the substance being assayed.