This paper aims at investigating various aspects of verbal derivation (alias 'extensions') found in contemporary Chadic languages, in terms of both synchrony and diachrony. The Chadic language family, which is a member of the Afroasiatic phylum, consists of ca. 150 languages distributed in northern Nigeria, northern Cameroon, southern Chad and southern Niger. Hausa is the most well known Chadic language as well as the biggest lingua franca in West Africa with its 45 million speakers (L1 + L2), whereas most other Chadic languages have less than 100,000 speakers. Also, while Hausa is boastful of more than 150 years research tradition, there still remain many Chadic languages unstudied. Drawing on data from 28 Chadic languages (18 core + 10 auxiliary), this paper investigates formal as well as functional characteristics of verbal extensions. More concretely, it focuses on the following aspects; 1) ways in which the authors describe and understand verbal extensions, 2) terminological issues, 3) formal and typological characteristics of extensions, 4) meanings and functional characteristics of extensions, 5) grammaticalization of extensions and 6) Proto-Chadic extensions. Since one of the main purposes of this study is to discover the whole formal characteristics of extensions used in Chadic, the discussion is not confined to dependent morphemes, although these are the most typical means to mark extensions. Therefore, as a cover term, 'extension' rather than 'derivation' is employed in this paper, comprising both dependent (affixes) as well as free grammatical morphemes (particles and adpositions). The whole discussion and analyses of extensions are based on the Chadic Extension Inventory (CEI) established for this study. The CEI includes all the information the individual authors provide in their grammatical descriptions regarding verbal extension, e.g. types and functions of extensions, terms, etymological information, etc. The CEI shows that the Chadic languages have developed a number of diverse extensions in the course of their long history. But, only the following extensions have relatively wide distributions across branches; ventive, centrifugal, causative, applicative, reflexive(passive), partitive, completive, totality. Among the languages investigated, the languages from the Central branch, especially C-A-3 and C-A-4, have a very rich system of extensions in contrast to other groups. Regarding marking devices for verbal extension, the Chadie languages typically use suffixes as many other African languages, whereas there are also languages that use free grammatical morphemes like particles or adposition. Infixes and other morphological processes (e.g. reduplication, consonant gemination, etc.) are also used for extending and modifying verbal meanings, though they are largely confined to marking verbal pluractionality. The use of prefix as an extension marker is very rare in Chadic. There are also a number of cases where lexical items have grammaticalized to extensional markers; e.g. 'to go' > centrifugal in Buduma and Dangaleat, 'mouth' > totality in Margi and Lamang, etc. In this study only the ventive emerges as a possible Proto-Chadie extension; it occurs in all the Chadic branches with a very similar suffix. Other extensions are formally so diverse that one can hardly reconstruct the proto-forms with any certainty.