Colonoscopy remains the gold standard for the screening of colorectal cancer (CRC) aiming to detect and remove any pre-cancerous lesion. Indeed, a high quality colonoscopy improves the adenoma detection rate and therefore can decrease both the incidence of CRC and its mortality [1,2]. However, the quality of colonoscopy is directly related to bowel preparation, while inadequate bowel preparation affects all aspects of colonoscopy including its diagnostic yield and accuracy [1,3]. An inadequately prepared colon may lead to missed adenomas, shorter surveillance intervals between colonoscopies, increased time of the procedure, canceled and rescheduled procedures, factors that will finally cause increased health cost and longer length of stay [1,[3], [4], [5]]. Despite the fact that suboptimal bowel preparation has been reported in approximatively as much as 20% of all colonoscopies [1,4,5], the European Society of Gastrointestinal Endoscopy (ESGE) recommends that at least 90% of individuals undergoing colonoscopy should present with adequate bowel preparation [3]. In this respect, different modifiable and nonmodifiable factors that may affect the quality of bowel preparation have been reported. These factors can be either patient-related such as comorbidities, medications, previous surgeries, age, or preparation-related factors including preparation to colonoscopy interval, amount of regimen consumption, etc. [5,6]. In an effort to identify individuals with a potential inadequate bowel preparation before colonoscopy aiming to apply measures to improve its quality, different predictive scores have been developed. In this narrative review we aim to summarize and provide an updated overview with critical appraisal of available predictive scores and models that have been developed to assess bowel preparation adequateness (see Table 1, Table 2).