Reading has several unique properties. One such property is the universal dependence of writing systems on language. According to the "Universal Grammar of Reading" (Perfetti, 2003), writing systems encode spoken language and as such, do not represent meaning directly independent of language, necessitating language in decoding and encoding meaning in print. Reading thus is the dynamic pursuit embedded in two interrelated systemsa language and its writing system-and its acquisition requires making links between the two systems. Inevitably, learning to read entails systematic deductions at two levels: the general mapping (uncovering which language element is directly encoded in each graphic symbol) and the mapping details (unpacking how the symbols are used to encode spoken words).When literacy learning occurs in a second language (L2), the demands for the required linkage building increase exponentially. Unlike monolingual fi rst language (L1) reading, L2 reading is crosslinguistic, involving two languages in virtually all of its operations. Because each instance of L2 learning to read comprises a distinct combination of languages, the mapping requirements vary both within and across learner groups. L2 reading is further compounded by additional sources of variances as it encompasses a wider range of learners, including those of different ages and with diverse language backgrounds, than does L1 reading. L2 reading research must take into account these multiple diversities and the resulting complexities uniquely associated with L2 reading development. This entry describes (a) how orthographic knowledge contributes to learning to read, (b) how this knowledge varies across languages, and (c) how the knowledge acquired in one language affects learning to read in another language.In this entry, the term, writing system, is used in reference to both the writing system of a language and an abstract type of writing system. In the latter sense, writing systems can be classifi ed into three types: alphabetic, syllabic, and logographic (Coulmas, 2003). In the alphabetic system, each symbol represents a phoneme, while, in the syllabary, individual symbols denote distinct syllables. In contrast, a logographic character corresponds holistically to the meaning and sound of an entire morpheme. Within each system, considerable variations exist in the specifi c details in which graphic symbols are physically placed in encoding spoken words. Orthography refers to these language-specifi c details, and has been defi ned as "the standardized variety of a given, language-specifi c, writing system" (Coulmas, 2003, p. 35). Finally, the term script refers to the graphic form of the symbols of a writing system. To illustrate, English and Russian writing systems are both alphabetic, but they differ in their scripts-the former employs the Roman script and the latter uses the Cyrillic. English and Spanish are alphabetic, both employing the Roman script, but differ orthographically in spelling conventions.