What is the Dark Matter?

Four fifths of the matter in the universe is made of something completely different from the "ordinary matter" we know and love. I will explain why this "dark matter" is an unavoidable ingredient to explain the universe as we observe it, and I will describe what the fundamental, particle nature of the dark matter could possibly consist of. I will then give an overview of strategies to search for dark matter as a particle, describe a few examples of possible hints of discovery, and outline ways forward in this exciting hunt.