Relativity is a damned hard subject to fully comprehend, but it is an important part of being an educated person. Without this knowledge, one can occasionally make a serious mistake in judgment and be dead wrong about certain things. David Mermin explains the necessary thinking in a beautiful, skillful way. I can't imagine his making it clearer or simpler, but nevertheless, it is a HARD bit of reasoning to master. This short book requires reading word-for-word and then some rereading, but this is not a burden. It is written with a light, pleasant touch that is a delight and I fully recommend it to anyone ready to make a serious effort at understanding the real world.