Lactococcus lactis (L. lactis) is a gram positive bacterium from LAB bacteria (LAB) with a long history of processing and production of dairy products. The unique properties of this bacterium include rapid growth, high cell density, usable in fermentation industry, without inclusion body, surface display, endotoxin free, no external protease activity, having the least internal protease activity, and most importantly the ability of extracellular protein secretion. Therefore, it is considered to be a safe and appropriate host for the production of eukaryotic recombinant proteins in research and industry. The bacterium is, a cellular factory for production of a wide range of protein antigens as a vaccine and, a suitable host for delivery of therapeutic proteins and biologically active molecules into cells. For this purpose, several expression vectors and bacteria strains have been designed to express and produce recombinant proteins, described in this review.