The aim of this study is to discuss the interaction of linguistic complexity andmorpho-syntactic development in foreign language learners. The analysis ofmorpho-syntactic structures was carried out within the framework of Processability Theory (Pienemann 1998). To capture the level of complexity we investigate the following: sentence length, subordination and nominal vs. verbal style.Oral and written data from four adult learners were collected over a period ofone year. The analysis of complexity and morpho-syntax suggests that learnerscan be divided into different types, such as: The Risk-taker, The Recycler andThe Careful and Thorough.