In this paper a short overview on observability analysis techniques for inertial navigation systems (INS) is given. There are two approaches in the INS observability analysis: algebraic and numerical analysis approaches. Algebraic analysis provides general observability properties for a class of vehicle motions. This approach is suitable for relatively simple motions. On the contrary, numerical analysis can be applied to any motions. However, in order to draw general observability properties from this approach, a considerable number of tests may be necessary. Analysis techniques are briefly introduced and their relations are given. An illustrative numerical example is presented on the analysis techniques.