A link to basics, history, pros/cons, who uses 3D printing, etc:

3D Hubs "Definitive Guide to 3D Printing"

3D Printing Articles

3D Printing Helps Mayo Clinic

3D Printing a Heart
First Smartphone Printer

Additive Manufacturing Technologies Infographic

3D Printing Videos
3D Printing Materials Guide (28 Types of Materials Used in 3D Printing!)

3D Printing Jigs & Fixtures
​(3D printed cars, plane wings, etc.)

3D Printing Related Sites

TINKERCAD: Web-based CAD program.  Easy to use for ALL ages!

Onshape: powerful, professional grade, web-based CAD program