FDM

Fused deposition modeling (FDM) is best suited for low-cost prototyping, where form and fit are more important than function.FDM produces parts one layer at a time by extruding a thermoplastic onto a build plate.

SLA

SLA (stereolithography) printers use a laser to UV cure specific areas of a resin tank to form a solid part one cross-section at a time. 

SLS

Selective laser sintering (SLS) produces parts with high accuracy and can print designs with complex geometry. A laser selectively sinters powder one layer at a time to form a solid part.

Material Jetting

Material jetting is considered the most accurate form of 3D printing. Because there is no heat involved in the printing process warping and shrinkage rarely occur.

Metal 3D printing

Metal printing (specifically DMLS and SLM) use a laser to selectively sinter or melt metal powder to produce metal parts.