Seventeen species of slugs and semi-slugs from northern Algeria are described and discussed. The species are provided with synonyms, brief descriptions of external characters and genitalia, distribution, and ecology. Some taxonomic and biogeographical issues are discussed, and a key to the species is given. The paper is based on the analysis of material collected in North Algeria between 2018 and 2022 and on a critical review of the available literature data. Ambigolimax parvipenis is recorded for the first time from Algeria. Limax brondelianus Bourguignat, 1861 is regarded as a valid species of Deroceras as D. cf. brondelianum comb. nov . Two new synonyms are proposed: Amalia cabiliana Pollonera, 1891, syn. nov . is proposed as a junior synonym of Milax gagates (Draparnaud, 1801); Ariunculus pallaryi Collinge, 1904, syn. nov . is proposed as a junior synonym of Letourneuxia nyctelia Bourguignat, 1861.