This chapter details the different approaches to markerless tracking and the components it requires,thatthepreviouschaptermentionedtosomeextent. First,section3.1presentsmodel- basedtracking. Asthisthesisdoesnotusemodel-basedtracking,thesectiongivesonlyarough overview. Approaches based on image processing and pattern recognition fill the rest of the chapter. Section 3.2 summarises the basic process and stages of these approaches. The follo- wing sections contemplate the different stages: section 3.3 depicts feature detection and des- cription,section3.4detailsthesearchforcorrespondences,section3.5elaboratesapproachesto pose estimation and section 3.6 explains 3D reconstruction. Section 3.7 introduces the concept ofSimultaneousLocalisationandMapping,whichintegratesthestagesintoanoverallconcept.