David Barrado Navascues LAEFF A Brown Dwarf is a quasi-stellar object unable to fuse hydrogen in a stable manner. This happens because its mass is so small (about seven percent of the solar mass, or seventy five the mass of Jupiter) that its core never gets hot and dense enough to initiate this nuclear reaction. Therefore, since its only source of energy is from its gravitational potential, a Brown Dwarf contracts and cools down with age, becoming fainter. I am conducting several research projects in this area, including the discovery and characterization of the Brown Dwarf properties located in the field and in young stellar asociations. One of my main targets has been the nearby young cluster associated to the Sigma Orionis star (about 5 million years old) and the Orion's Head (Lambda Orionis or Collinder 69), of similar age. I have used different techniques, from optical and near- and mid-infrared photometry and spectroscopy to X-ray, using both ground based and space telescopes. A key problem is the formation mechanism of brown dwarfs. They might form either in similar fashion to stars or as planets. See the webpage of the Star Formation Group at LAEFF (www.laeff.inta.es) or the formation and evolution of Planetary Systems. We are dealing with this problem from different perspectives, such as substellar Initial Mass Function or the spatial distribution in an open cluster. Another, related problem is Brown Dwarfs with accreting disks. In addition, I am conducting several studies regarding the properties of solar and low-mass stars belonging to different open clusters, trying to undertand the evolution of several stellar properties such as lithium, rotation and activity. Finally, I am involved in several instrument developments, such as MIRI (for JWST) and NAHUAL (for the Spanish 10m telescope). --------------