A short guide to one of the most celebrated diagrams in the history of science, a tool for understanding the basic building blocks of the universe.

What is the periodic table? -- The history of the periodic table -- What elements are made of -- Alkali metals and alkaline earth metals -- Transition metals -- Lanthanides, actinides, and transuranium elements -- Poor metals, metalloids, and nonmetals: the BCNOs -- Halogens and noble gases -- At the table's edge.