 From 2006 to 2011, an average of 15 novel recombinant protein therapeutics have been approved by U.S. Food and Drug Administration, FDA, annually. Increasing numbers of innovator biologic products and biosimilars have fueled the demand of production cell lines with high productivity. This article reviews established advances in protein expression and clone screening which are the core technologies in mammalian cell line development. Advancements in these component technologies are vital to improve the speed and efficiency. This article was authored by Sae Kong-ing, Ting Fung Lai, and Yu An-cheng Yang.