The main objective of foreign language learning and teaching is the development of communicative language competence. One of its key components is discourse competence which consists of three main elements: cohesion, coherence and text composition (Bagarić Medve and Pavičić Takač 2013). The development of writing skills is acknowledged as one of the main challenges in foreign language learning and teaching, which includes the appropriate usage of cohesive devices in order to tackle the semantic relationships within a text. In German, explicit cohesive devices refer to coordinating conjunctions, subordinating conjunctions and adverbial connectors. While a bulk of previous research has focused on English as a foreign language, the studies conducted among the learners of German are still scarce Earlier studies (e.g. Breindl 2016; Vaakanainen and Maijala 2022) pointed to a limited range of variations within the same semantic group and an inappropriate use of connectives when comparing their usage between native speakers and learners of German as a foreign language (GFL). The aim of the present study is to analyse the frequency, variation and errors of causal and additive connectives (coordinating conjunctions, subordinating conjunctions and adverbial connectors) in GFL argumentative writing. The corpus consists of 43 argumentative essays written by Croatian GFL students at B2 level. The findings concerning frequency show that additional connectives are most frequently used within the whole corpus, whereas causal connectives take third place. The additive coordinating conjunction und is the most frequent additive item, the subordinating conjunction weil is the most frequently used causal item. The results connected to variation point to a wider range in the use of additional connectives in comparison to causal, but also reveal more error recognition within the additive semantic group. The most common types of errors concerning connectors detected in the corpus are as follows: syntax, meaning, spelling/punctuation, redundancy and register. In order to utilize these research findings aiming at improving the writing skills of GFL students in the learning/instructional process, practical implications are presented at the end.