A group of German philosophers who worked to develop a unified critical theory, first in Frankfurt, Germany (in the 1930s) and later in the United States.

Trend of philosophical thought, also often called "neopositivism" and "logical empiricism," which began in the 1920s with the Vienna Circle. Its key tenet was the verifiability criterion, according to which no statement has any meaning beyond the manner in which it is verified.

Links to sites dedicated to individual 20th-century philosophers. These sites will typically contain works by or about a philosopher.