While the industrial use of bamboo stretches back at least thousands of years, the modern use of bamboo in textiles is a very recent development (enabled by advancing technology). Originally, bamboo's applications for clothing were limited to corset ribs, bustles and armor, but today we get to enjoy many much more conventional fibers produced by this material.
It is inexpensive, it is tough and it can be surprisingly soft (especially when one considers the source). A retting process similar to that used to produce fiber from hemp mechanically breaks down the woody part of the bamboo, leaving a silky bast fiber behind that can then be spun into yarn. And speaking of silk, bamboo is very drapey when knit - making it an excellent candidate for those looking for an alternative to silk.
As with hemp, bamboo is a fantastic plant to harvest in terms of its yield, growth rate and resource requirements. It is the fastest growing woody plant on Earth, reaching its full height (of up to 35 meters) just eight to ten weeks after being planted, ultimately yielding upwards of 60 tons of material per year per hectare.
This is a textile that is only going to become more important in coming years as we strive to be live more sustainably and be more considerate about our impact on our environment.