“Diet beverage” is a common term used to describe beverages that are sweetened with non-nutritive or artificial sweeteners (ASBs). Marketing strategies often imply that consuming these beverages holds promise for weight control or weight loss. The objective of the present review is to provide a synthesis of the literature on the effects of ASBs on body weight, cardiovascular disease, and type 2 diabetes. Consumption of diet beverages is much lower than that of sugar-sweetened beverages (SSBs), and people trying to lose weight report the highest levels of ASB consumption. To date, prospective observational studies have revealed mixed results, and it appears that reverse causality is a particular problem, since individuals who are at higher risk for weight gain may choose to consume ASBs in an attempt to control their weight or reduce disease risk. As for experimental studies, the evidence currently suggests that obesity risk may be lower when ASBs replace SSBs in the diet. Still, additional evidence from experimental studies is needed to more definitively determine the benefits and risks of frequent ASB consumption.