Background: There is much interest from stakeholders in understanding how health technology assessment (HTA) committees make national funding decisions for health technologies. A growing literature has analysed past decisions by committees (revealed preference, RP studies) and hypothetical decisions by committee members (stated preference, SP studies) to identify factors influencing decisions and assess their importance. Objectives: A systematic review of the literature was undertaken to provide insight into committee preferences for these factors (after controlling for other factors) and the methods used to elicit them. Methods: Ovid Medline, Embase, Econlit and Web of Science were searched from inception to 11 May 2017. Included studies had to have investigated factors considered by HTA committees and to have conducted multivariate analysis to identify the effect of each factor on funding decisions. Factors were classified as being important based on statistical significance, and their impact on decisions was compared using marginal effects. Results: Twenty-three RP and four SP studies (containing 42 analyses) of 14 HTA committees met the inclusion criteria. Although factors were defined differently, the SP literature generally found clinical efficacy, cost-effectiveness and equity factors (such as disease severity) were each important to the Pharmaceutical Benefits Advisory Committee (PBAC), the National Institute for Health and Care Excellence (NICE) and the All Wales Medicines Strategy Group. These findings were supported by the RP studies of the PBAC, but not the other committees, which found funding decisions by these and other committees were mostly influenced by the acceptance of the clinical evidence and, where applicable, cost-effectiveness. Trust in the evidence was very important for decision makers, equivalent to reducing the incremental cost-effectiveness ratio (cost per quality-adjusted life-year) by A$38,000 (Australian dollars) for the PBAC and £15,000 for NICE. Conclusions: This review found trust in the clinical evidence and, where applicable, cost-effectiveness were important for decision makers. Many methodological differences likely contributed to the diversity in some of the other findings across studies of the same committee. Further work is needed to better understand how competing factors are valued by different HTA committees.