Husserl's philosophy of mathematics is interpreted as dealing with forms not unlike Aristotle's forms. They can be somehow immediately present in one's consciousness. Husserl's ideas are compared for similarities and dissimilarities with those of Aristotle, Mach, Russell and Wittgenstein. Husserl's main development is seen as making these forms more and more robust conceptually. It parallels the overall development of mathematics in the last 200 years from a study of numbers and space into a study of different structures. This development culminates in Husserl's unfinished project of a theory of all theories. This project has closer connections with Hilbert's axiomatic theorizing than with the ideas of the intuitionists.