Response to Intervention (RTI) models of reading instruction have received much attention in the literature (Fuchs, Mock, Morgan, & Young, 2003; Hosp & Ardoin, 2008; Justice, 2006). Such models call for frequent and high-quality assessment of students' skills. One skill that is vital in the process of learning to read is the ability to sound out letters and blend these sounds together to produce a word. According to Dual Route models of reading (e.g., Coltheart, Rastle, Perry, Langdon, & Ziegler, 2001), these skills comprise the sublexical route to reading. This is best assessed by tests of nonword reading. In this article, 17 tests of nonword reading were reviewed in light of RTI and Dual Route models. The aim of the review was to determine the best available nonword reading tests for use at the Tier One and Tier Two levels of intervention, and the best available nonword reading test for diagnostic (Tier Three) purposes. The review determined that several good-quality tests of nonword reading, suitable for assessing the general functioning of the sublexical route to reading (at the Tier One and Tier Two level), are available, but that no test of nonword reading is available that fulfils all of the desirable criteria for a Tier Three, diagnostic assessment.