3D printing is a process for the production of physical objects usually by directing a laser to fuse a plastic powder one micro-layer at a time. The method can be used to create prototypes from CAD software. Custom designed figurines or sculptures are possible. Numerous other applications are under development.
Quillnpenn provided a list of references as follows-- 
Motley Fool has a tag archive on the subject-- 
Quillnpenn lists players as--
Stock Ticker PE $/sh Notes
Stratasys, Inc. SSYS 76 42 3D printers, prototyping systems
3D Systems Corp. DDD 69 30 3D printers
Autodesk, Inc. ADSK 28 15 3D software
Organovo Holdings, Inc. ONVO NA NA 3D human tissue printing
Dassault Systèmes SA DASTY 31 NA SolidWorks 3D CAD program
Parametric Technology, now PTC Inc. PMTC 31 13 Product Design software solutions
3DIcon Corporation TDCP NA NA Optical holographic technologies (Penny stock. Shares quoted at less than 0.001/share.)
Trimble TRMB 37 16 3D modeling package
Siemens SI 16 12 Solid Edge 3D software, NX CAM software
MakerBot LLC of Brooklyn, NY is offering desktop 3D printers for about $2200. They opened a store in New York City in November, 2012. [] MakerBot claims abt 20% market share of printing equipment. Acquired by Stratasys in 2013.
"At least seven 3D printer companies are exhibiting at CES [the Consumer Electronics Show in Jan, 2013 in Las Vegas], including 3D Systems (DDD), Stratasys (SSYS), MakerBot Industries and Formlabs." Read More At IBD: []
Voxeljet AG, ticker VJET. German company sells both printers and supplies and provides prototyping services.
Proto Labs. ticker PRLB. Fineline product offers precision rapid prototyping by additive manufacturing.
Materialise (NASDAQ:MTLS) 3D printing software and services.
Hewlett-Packard, ticker HPQ, is reportedly readying a 3D printer using its ink jet printing technology. It is planned for release in 2016.
In 2015, Eastman Chemical announced Amphora branded thermoplastic media for 3D printing. They report working with 3D printing filament provider taulman 3D and desktop 3D printer developer Aleph Objects, Inc. Helian of Netherlands, owner of ColorFabb, a medium for the Stacker, low cost 3D printer is another user of Amphora. Carbon fiber media is also available.
Taulman 3D is a leading supplier of thermoplastic materials for 3D printing. . The company appears to be privately held. Efforts to develop improved materials appears to be in process.
Aleph Objects is a manufacturer of 3D printers located in Lovelace, CO. 
Helian of Netherlands specializes in master batches of thermoplastics making possible unique colors and customized blends with additives. 
Stacker is a low cost 3D printer financed by crowdfunding on Kickstarter. First production is due in May, 2015. 
Voxel8 is a 3D printing startup that uses electrically conductive silver ink to fabricate complex electronic circuitboards.
According to C&EN, Wohlers Associates says 3D printing is averaging 34% annual growth for three years reaching $4.1B for materials and equipment in 2014.
C&EN reports that Evonik has been a leading supplier of Nylon 12 for laser sintering. Nylon 12 is a specialty product which has had supply limitations due to shortages of a key intermediate. BASF is developing Nylon 6 powder. This is a common nylon, usually used in tire cords.
Sisma Group is a producer of precision laser equipment used for 3D printing of metal powders. The method is well suited to use with precious metals for production of dental work or jewelry.  Video:  Sisma is located in Rocchette, Italy but appears to be privately held. This is sometimes called 3D metal.
Related Fool Discussion Boards
Post your questions on Motley Fool's "3D Printing" board.
Recent Mentions on Fool.com
- 3 Things Seagate Technology PLC Management Wants You to Know
- Why Did Apple Inc. Buy This "Star Wars"-Related Company?
- 5 Hot Healthcare Trends We Won't Be Able to Get Enough of in 2016
- 3 Reasons Proto Labs, Inc. Is Crushing 3D Systems and Stratasys in 2015
- Apple Inc. iPhone 7 Specs: Here's What to Expect
- Stocks to Watch in Dental Products: Henry Schein Inc. and Sirona Dental Systems Inc.