Galileo is credited with introducing the world to the two most important aspects of modern science: its research methods and its criterion of truth. He was the first major figure to defend a scientist's right to conduct research through observation and experimentation without being influenced by considerations outside of science, such as politics and theology.

Galileo attacked the pseudoscientists of his era and addressed his writings to the general public. His support for Copernican cosmology in the face of the Church's strong opposition, his invention of the telescope, his observation of phenomena like comets and sunspots, and his unconventional views as a philosopher of science were all central concerns in his scientific life and the subjects of four of his most important works.