Text simplification (TS) reduces the complexity of the text to improve its readability and understandability, while possibly retaining its original information content. Over time, TS has become an essential tool in helping those with low literacy levels, non-native learners, and those struggling with various types of reading comprehension problems. In addition, it is used in a preprocessing stage to enhance other NLP tasks. This survey presents an extensive study of current research studies in the field of TS, as well as covering resources, corpora, and evaluation methods that have been used in those studies.