Stereolithography (SLA)
This was the first 3D printing technology to be developed. It uses a stereolithograph apparatus to transform liquid material into a solid printed object. Digital light processing (DLP) is very similar.
Selective laser sintering (SLS)
Selective laser sintering is similar to stereolithography, but uses powdered material (stereolithography uses a liquid resin). Selective laser melting (SLM) is a subcategory of this type of 3D printing process, and Electronic Beam Melting (EBM) is another, though it uses an electron beam instead of a laser.