**1. Introduction**

Alginate has been extensively used for tissue engineering and regenerative medicine purposes [1]. Its ability to form hydrogels under mild gelation conditions in the presence of ions such as Ca2+, Ba2+, and Sr2+ renders it suitable for cell-based applications where exposure to harsh crosslinking buffers can lead to cell damage. When alginate is exposed to a crosslinking solution, l-guluronic residues of adjacent polysaccharide strands are connected forming a hydrogel [2, 3]. Alginate hydrogels possess the advantages of natural biomaterials such as excellent biocompatibility and abundance in nature with a low cost, properties which render it an excellent candidate for cell-based regenerative medicine applications [4]. However, the lack of alginate bioactivity requires functionalization with a wide variety of molecules promoting adhesion and modulation of stem cell fate. The purpose of this chapter is to provide an overview of the use of alginate hydrogels with mesenchymal stem cells (MSCs) which represent one of the most widely used stem cell type and the only stem cell type currently in clinical use.
