  This primarily expository article collects together some facts from the
literature about the monodromy of differential equations on a p-adic (rigid
analytic) annulus, though often with simpler proofs. These include Matsuda's
classification of quasi-unipotent nabla-modules, the Christol-Mebkhout
construction of the ramification filtration, and the Christol-Dwork Frobenius
antecedent theorem. We also briefly discuss the p-adic local monodromy theorem
without proof.
