Errors are systematic deviations which occur as a result of lack of knowledge and are associated with failure in competence. Even though lexis plays an important role in language learning and lexical errors are a significant problem in EFL learners' writing, little academic time has been spent analysing the types of errors learners make with their word choice. Using the Error Analysis Approach, the book explores the various types of lexical errors frequently occurring in the writing of Egyptian EFL learners and attempts to explain the possible sources of these errors, whether interlingual (L1-based) or intralingual (L2-based). Such error analysis plays an important role in learning more about the process of second language acquisition and can usefully inform ESL/EFL teachers and researchers working with learners from many different backgrounds about the type and range of lexical errors that need attention and hence can devise new methods and strategies to deal with them.