The sigma Orionis cluster is a natural laboratory to study stars and protoplanetary disks in the first stages of their evolution. This cluster is relatively near (distance ~400 pc) and the extinction is low (Av ~<0.5 mag), enabling us to study young stars over a wide range of masses, from its most massive central star, sigma Ori AB (O9.5 type star), to the lowest mass objects, such as brown dwarfs and free-floating planets. Recently, we have carried out the most comprehensive and homogeneous spectroscopic characterization of stars belonging to this cluster. This study is a corner stone for deriving stellar parameters. Of particular interest are stars that exhibit infrared excesses produced by protoplanetary disks. Since the sigma Orionis cluster is at an evolutionary stage in which one third of its members still have disks, and additionally the mechanisms of disk dispersal have affected substantially its disk population, we observe a large diversity of protoplanetary disks. Particularly, we can see optically thick full disks, pre-transitional disks, transitional disks, homogeneously depleted disks (evolved disks) and second generation debris disks.