One of the main characteristics of Tehrani varietyVariety of Persian is thePre-nasal raisingpre-nasal vowel raising process of pre-nasal vowel raisingPre-nasal raisingpre-nasal vowel where /ɑ/ (the target segmentTarget segment) raises to [u] when it is immediately followed by a nasal consonantNasal consonant (the trigger segmentTrigger segment). This study presents an overview of this process in Tehrani PersianTehrani Persian and shows that there are three main categories of phonological, morphological, and lexical factors that block the raising alternationAlternation. The goal of this study is to show that to account for some phonological processesPhonological processes, such asPre-nasal raisingpre-nasal vowel raising pre-nasal vowel raisingPre-nasal raisingpre-nasal vowel, the role of multiple factors should be taken into consideration. Prior to the discussion of these blocking factors, in Sect. 1, the vowel raisingVowel raising process is introduced. Section 2 provides a description of a databaseDatabase containing words with the /ɑ/ and the nasal consonantNasal consonant sequence. In Sects. 3, 4, and 5 the phonological, morphological, and lexical factors that block the occurrence of the pre-nasal raising are discussed, respectively. Section 6 discusses the interaction of these three factors. In Sect. 7, the blocking factors are categorized in a hierarchical order based on the number of exceptionsException each blocker encounters. After the conclusion in Sect. 8, the chapter ends with suggestions for future studies.