Thermoluminescence dosimetry (TLD) is a versatile tool for the assessment of dose from ionising radiation. The wide variety of TLD materials and their different physical forms allow the determination of different radiation qualities at dose levels from microGy to kGy. Major advantages of TL dosimeters are their small physical size and that no cables or auxiliary equipment is required during the dose measurement. This makes them well suited for a wide range of applications in medicine. However, while larger institutions with extensive experience in TLD commonly achieve quite good results, thermoluminescence dosimetry appears a bit like a black art for physicists who attempt to set up a TLD system for the first time. Therefore, the present article aims at summarising the relevant literature describing problems and possible pitfalls in the evaluation of TLD readings. The second part of the review (to be published) will discuss typical applications of TLD in medicine. Most applications and the major part of the literature are based on lithium fluoride doped with magnesium and titanium (LiF:Mg,Ti). However, other materials such as CaSO4:Dy are widely used, and some more recent TL materials such as LiF:Mg,Cu,P show great potential for radiation dosimetry. Therefore, the present article while focusing on LiF:Mg,Ti also includes other TLD materials of interest for dosimetry in the medical field. Furthermore, TLD apparatus and a variety of TLD applications and techniques shall be discussed with two intentions: firstly to give an update of TLD in medicine, and secondly to enable readers to set up or optimise their own TLD system.