In everyday communication, changing the word order of a sentence is a helpful resource to enhance expressiveness. However, such a resource comes with a cost: in languages like Russian and Italian, which allow great variation in word order, constituents must be marked by case or verb agreement, otherwise the propositional content is at risk. While this cost is fully affordable for native speakers, it is taxing indeed for L2 learners. This work sketches out the path towards the acquisition of marked (i.e. non-canonical) word orders in L2 Russian and Italian. The book provides a formal description of these structures, pointing out different approaches in linguistic theory and their (dis)advantages in L2 learning; then it discusses grammatical progress by revisiting the framework of Processability Theory, providing sound developmental hypotheses, and testing them out with fresh crosssectional data. Results reveal interesting patterns, useful for both L2 learners in self-assessing their point of development, and L2 teachers in constructing an effective, theoretically-founded syllabus.