The verbs of the ‘to be’-group, also called verba substantiva, belong to the most enigmatic phenomena of the human language. Combining a distinct suppletivity of their conjugational forms in most languages with a striking semantic and functional ambiguity, as well as unique syntactic capabilities, they form a very specific class of linguistic entities. They can be referred to, without exaggeration, as one of the conceptually gravest and most ‘symptomatic’ language formations. Typologically, the be-verbs demonstrate, on the one hand, a set of similar features in almost every language, which is excellent evidence of their universal validity. On the other hand, the differences between these verbs in various language groups and even in particular languages are remarkable proof of language relativism. Historically, the be-verbs show a sequence of relevant stages in their formal, semantic and syntactic developments, which in many aspects coincide with their typological and individual, ‘idioethnic’ features and properties. One can trace, among other things, paths and mechanisms of their development and salient changes of their functions in language systems of different types. Especially important are also changes in the form and function of the be-verbs arising from language contact, for they indicate essential tendencies in the evolution of these entities accelerated by the influence of language interaction triggers. The contribution of to be-verbs to the morphology, semantics and syntax of the majority of the languages of the world is substantial from a number of perspectives, and these verbs belong to the most complex and simultaneously central entities of human language. For this reason their analysis must continually be synchronized with the newest results of general linguistic research. This volume, hence, describes and interprets the to be-verbs and constructions in the broad context of contemporary linguistic research, including synchrony, diachrony, diatopy, language contrast and typology.