This chapter introduces hydrogen (H) mappingMapping and depthProfiling profilingDepth profile obtained by either TARGTritium Auto Radiography (TARG) (tritium autoradiography), TIPT (tritium imaging plate technique), Kelvin probe, Ag decoration or microprinting, electrochemical technique and some others. They show localized high H accumulationH accumulation at various locations; metallic inclusionsInclusion (impurities), precipitatesPrecipitate like carbideCarbide, oxides and sulfideSulfides, their boundaries with matrix, slip planesSlip plane, twin boundariesTwin boundaries, grain boundaries and so on. However, it should be noted that the H mappingH mapping is just a snap shot at a particular time and in a specified condition in the amount of H, temperature, surrounding atmosphere, and so on. Above RT or at ambient temperature, H in a metal easily moves to change its profiles on surface and in depth. Therefore, it is still difficult to mention that the highly H accumulated sites really trap H to be immobilized or that H preferentially passes through the sites or is enhanced to migrate like short path diffusion. Although the amount of trapped HTrapped H in a local trappingTrapping siteTrapping site seems much larger compared to the dissolved HDissolved H in the surrounding matrix area, the integrated amount of dissolved HDissolved H in the matrix could be larger and dynamic exchange of T between trapped one and dissolved one likely occurs. Therefore, simultaneous observation of trapped H and dissolved H is necessary and their time sequences are quite important for correct understanding of H kineticsKinetics, which is one of the most important massages of this book.