This book presents a comprehensive investigation into the acquisition of Arabic as a second language. It has two primary objectives: first to establish the developmental sequence for the acquisition of Arabic interlanguage morphology and syntax; second to investigate cross-linguistically certain claims and principles proposed in Pienemann's (1998) Processability theory. This second objective is particularly important as it explores issues of language processing and language development (Clahsen 1984; Pienemann 1998) in a second language acquisition (SLA) context where the target language (Arabic) is typologically different to those languages previously investigated, in particular, English, German and Spanish. The main research questions stem from: Processability-related SLA research (Pienemann 1994, 1998; Johnston 1995; Andersen 1991); Arabic L1 research (Omar 1973); and Arabic SLA research (Al-Buanain 1987; Mansouri 1995, 1997). With regard to the morpho-syntactic predictions generated through Processability-related research, the findings of this study are consistent with those reported by Pienemann (1994) and Johnston (1995) on the acquisition of German and Spanish respectively. However, the findings that relate to interlanguage morphology are less consistent with the Processability-generated predictions.