Background and Objective. The most frequently used methods for assessing pain are self-reports and observation. However, physiological methods could improve accuracy and reliability for those with communicative difficulties. This review's objective is to analyze methods used to physiologically assess pain, to rank them by invasiveness per method and vulnerability per subject group, and to assess their technological maturity. Databases and Data Treatment. Six international databases were searched for review papers between 2007 and 2019. Inclusion criteria were as follows: at least one physiological method for acute or chronic pain in humans; languages were as follows: English, French, Dutch, German, and Spanish. Quality of reviews was assessed using the CASP checklist. Results. The methods' heart rate variability and electroencephalogram show clear and consistent results as acute pain assessment. Magnetic resonance imaging can measure chronic pain. Ordered by invasiveness and vulnerability, a trend shows that the invasive methods are used more with less vulnerable subjects. Only instruments used for skin conductance and automatic facial recognition have a lower-than-average technological maturity. Conclusions. Some pain assessment methods show good and consistent results and have high technological maturity; however, using them as pain assessment for persons with ID is uncommon. Since this addition can ameliorate caregiving, more research of assessment methods should occur.