Ectoine, a natural osmolyte that stabilizes proteins, membranes, and whole cells, is used in cosmetics, foods, and biopharmaceutical formulations. Traditional production relies on salt-rich batch fermentation of native halophiles, which limits scalability and sustainability. This chapter reviews the recent breakthroughs in reshaping the field. Engineered Halomonas now achieves >20 g L−1 ectoine in non-sterile, low-salt air-lift reactors. In parallel, multi-layered pathway balancing enables Escherichia coli and Corynebacterium glutamicum to produce >130 g L−1 from renewable feedstocks. Advances in Pichia pastoris and cell-free systems have further reduced salinity constraints, simplifying downstream purification. Techno-economic and life-cycle assessments indicate the potential to lower the cost of goods below US$10 kg−1, positioning ectoine as a flagship molecule for circular, seawater-based fermentation systems.