Despite the ubiquitous practice of environmental impact assessment around the world, socialimpact assessment has been alienated from assessment process from the beginning. Not until1993 was ‘Interorganizational Committee’ established in the United States to prepare for‘Principles and Guidelines for Social Impact Assessment.’ This study is an attempt to criticallyexamine US ‘Principles and Guidelines.’ First, the study traces history of social impactassessment to reveal why the latter became “the orphan in the assessment process.” Second, itcritically reviews ‘Principles and Guidelines’ to find its merits and defects. For instance, aprinciple regarding environmental justice is perceived as necessary as society has becomeconscious of social justice and equity while putting too much emphasis on predictive traits ofsocial impact assessments only fosters “checklist mentality.” Third, the study reflects on‘Principles and Guidelines’ in particular and social impact assessment in general in order toprobe what is social impact assessment. To do so, it pays attention to scholars, who havecriticized technocratic and procedural elements of ‘Principles and Guidelines.’ They show thatsocial impact assessment is philosophically and methodologically teleological in that “fluid andcontested meanings” between social impacts and the public are meaningful in itself. Andsimple procedural guarantee of the public involvement, they argue, is not enough to definesocial impacts. Lastly, from the critical analysis of ‘Principles and Guideline,’ the study looks foralternatives to improve how to assess social impacts in a Korean context.