This document appears to be a thesis written by J. Rogelio P ́erez Buend ́ıa on giving a criterion for determining whether an algebraic K3-surface over a p-adic field has good reduction based on its p-adic étale cohomology. The objective is to show that a K3-surface has good reduction if and only if its second étale cohomology group is crystalline. Notations and examples of K3-surfaces and p-adic representations are provided. The document also discusses Fontaine's construction of ring of periods to establish comparison isomorphisms between cohomology theories in the p-adic setting.