Spelling error corpora can be collected from students' written essays, homework, dictations, translations, tests and lecture notes. Spelling errors can be classified into whole word errors, faulty graphemes and faulty phonemes in which graphemes are deleted, added, reversed or substituted. They can be used for identifying phonological and orthographic problems; spelling strategies that EFL students use in spelling English; spelling error causes or sources and relationship between spelling and decoding weaknesses. The paper gives examples of spelling errors and shows how spelling errors are quantified. Recommendations for remediation are also given.