Lactococcus lactis is used throughout the world for the production of fermented milk products like cheese and buttermilk, and for the production of food ingredients. It plays an essential role in food preservation and contributes to the nutritional, sensoric and health properties of the products. Due to their world-wide importance, lactic acid bacteria (LAB), and L. lactis in particular, have attracted a host of scientific interest over the last three decades by academic research groups as well as by industry. By now, L. lactis is the most transparent of the LAB: its genetic amenability has allowed answering many research questions. Some of that work has been used to improve traditional applications of L. lactis but it has also resulted in exiting novel possibilities of using e.g., L. lactis for entirely new applications such as for the production of (oral) vaccines and for the local production (in the human body) of medically relevant proteins/peptides.