The purpose of this research was to probe the philosophical beliefs of instructional designers using sound philosophical constructs and quantitative data collection and analysis. We investigated the philosophical and methodological beliefs of instructional designers, including 152 instructional design faculty members and 118 non-faculty professionals. We used the Philosophy of Social Science Inventory, a 52-item questionnaire, to measure 20 beliefs within four categories. We probed four ontological beliefs (ontological realism, ontological relativism, physicalism, and idealism); five epistemological beliefs (epistemological relativism, fallibilism, epistemological objectivity, rationalism, and empiricism); three axiological beliefs (ethical realism, ethical relativism, and valueneutrality in research); and eight methodological beliefs (nomothetic, idiographic and critical methods, scientific naturalism, humanism, and quantitative, qualitative and mixed methods). Our research questions included (a) What are the predominant philosophical and methodological beliefs of instructional designers? (b) Do instructional design faculty and non-faculty instructional designers, identifying with different research methodologies, hold different sets of philosophical beliefs? and (c) What relationships exist between philosophical beliefs and age, gender, ethnicity, level of education, and/or years of service? Overall, the philosophical profile of instructional designers can reasonably be described as pragmatic. Belief characterizations of methodological subgroups (e.g., those identifying with qualitative, quantitative, or mixed methods research) generally supported our hypotheses. Although demographic variables (except gender) were not singularly important, our analyses suggest that a combination of ethnicity, gender, research preference, and level of education can be used to predict philosophical and methodological beliefs.