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If there is a movement or school that epitomizes analytic philosophy in the middle of the twentieth century, it is logical empiricism. Logical empiricists created a scientifically and technically informed philosophy of science, established mathematical logic as a topic in and tool for philosophy, and initiated the project of formal semantics. Accounts of analytic philosophy written in the middle of the twentieth century gave logical empiricism a central place in the project. The second wave of interpretative accounts was constructed to show how philosophy should progress, or had progressed, beyond logical empiricism. The essays survey the formative stages of logical empiricism in central Europe and its acculturation in North America, discussing its main topics, and achievements and failures, in different areas of philosophy of science, and assessing its influence on philosophy, past, present, and future.