The complex diachronic and synchronic status of the concepts be and have can be understood only with consideration of their full range of constructions and functions. Data from modern Slavic languages (Russian, Czech, Polish, Bulgarian) provides a window into zero copulas, non-verbal have expressions, and verbal constructions. From the perspective of cognitive linguistics, be and have are analyzed in terms of a blended prototype model, wherein existence/copula for be and possession/relationship for have are inseparably combined. These concepts are related to each other in their functions and meanings and serve as organizing principles in a conceptual network of semantic neighbors, including give, take, get, become, make, and verbs of position and motion. Renewal and replacement of be and have occur through processes of polysemization and suppletization involving lexical items in this network. Topics include polysemy, suppletion, tense/mood auxiliaries, modality, causatives, evidentiality, function words, contact phenomena, syntactic calques, and idiomatic constructions.