Every infinite-series problem on a Calc 2 or AP Calc BC exam comes down to picking the right test. This guide walks through the partial-sum definition of convergence and the harmonic counter-example, the nth-term divergence test, the two benchmark families (geometric series and p-series), the integral test (and how it proves the p-series rule), direct comparison and limit comparison against known benchmarks, the ratio and root tests for factorials and exponentials, the alternating series test with its error bound, the difference between absolute and conditional convergence, and a decision tree for choosing the right test the first time — with worked examples for each.