In experimental research, internal validity refers to what extent researchers can conclude that changes in dependent variable (i.e. outcome) are caused by manipulations in independent variable. The causal inference permits researchers to meaningfully interpret research results. This article discusses (a) internal validity threats in social and educational research using examples from the contemporary literature, and (b) research designs in terms of their ability to control various internal validity threats. An Eric and psychinfo search was performed to retrieve articles regarding this internal validity review. In conclusion, an appropriate research design that control possible extraneous variables is needed to be able meaningfully interpret research results. Although pretest-posttest experimental-control group design controls most of internal validity threats, the most appropriate research design would vary based on the research questions or goals.