We give a modern account of Agafonov’s original proof of his eponymous theorem. The original proof was only reported in Russian in a journal not widely available, and the work most commonly cited in western literature is instead the English translation of a summary version containing no proofs, and the main proof relied heavily on material well-known in Russian mathematical circles of the day, which perhaps obscures the main thrust of argumentation for modern readers. Our present account recasts Aganofov’s arguments using more basic building blocks than in the original proof, and contains some further embellishments to Agafonov’s original arguments, made in the interest of clarity. We posit that the modern account provides new insight to the underlying phenomena of the theorem. We also provides some historical context to Agafonov’s work, including a short de- scription of some of the ideas that led to Agafonov’s own proof, especially emphasizing the important work of Postnikova.