Glass

Glass is a decorative fully transparent block which can be dyed into stained glass.

Obtaining
Glass will only drop itself if it is broken with a tool enchanted with silk touch; otherwise it will drop nothing.

Trading
Villager librarians will trade 3 to 5 glass for 1 emerald as part of their tier 3 trades.

Natural generation
As of 1.9, magenta stained glass naturally generates as windows in end cities.

Usage
Most blocks that require placement on a solid block cannot be placed on glass or stained glass. The only exceptions are torches and redstone torches, which can be placed on top of glass, but not attached to their sides.

Glass blocks adjacent to other glass blocks are invisible when viewed through glass.