This book presents a juxtaposition of studies conducted in different proficiency groups (elementary, intermediate and advanced) among Polish students studying English. The theoretical section of the book discusses all necessary theories, both from a diachronic and a synchronic perspective, related to the acquisition of the English article system in both L1 and L2. The empirical part of the book concerns the studies carried out among Polish study participants. The results of the studies indicate that L2 Polish users acquire the English article system better as their linguistic competences advance. These outcomes prove that L2 acquisition of the English article system is facilitated better in the advanced group of subjects in contrast to the least advanced group, which had tremendous difficulties with the acquisition and subsequent relevant use of the English article system.