1. INTRODUCTION Writing in one's mother tongue is a demanding task that calls upon several language abilities, as well as upon more general (meta) cognitive abilities. Writing in a second language (L2) is even more demanding, because several of these constituent abilities may be less well developed than in one's first language (L1). Therefore, over the past twenty years, a large number of investigations have been carried out to identify the factors influencing L2 writing. Specifically, investigations of the relationship among L1 writing ability, L2 writing ability, and L2 proficiency have been widely conducted, among which some argued L1 writing ability as the main factor influencing L2 writing (Raimes, 1985; Zamel, 1983), while some others claimed L2 proficiency as the primary influencing factor (Pennington & So, 1993; Sasaki & Hirose, 1996), and still others proposed the interactive effects of the two. Their findings are mixed and lack consensus. The following are ten empirical studies selected from the literature on the relationship between L1 and L2 writing for research methods investigation.