Rudolf Steiner gave more than 6,000 lectures in Europe during the early part of the 20th century.  There were several topics on which he  published books.  Some of these  are listed here.  For more complete lists please visit:

STEINER BOOKS at www.steinerbooks.org

RUDOLF STEINER ARCHIVE at www.rsarchive.org

RUDOLF STEINER WEB at www.rudolfsteinerweb.com  

The Philosophy of Freedom  aka The Philosophy of Spiritual Activity aka Intuitive Thinking as a Spiritual Path .

How To Know Higher Worlds,                    (PREVIOUSLY KNOWN AS KNOWLEDGE OF THE HIGHER  WORLDS AND ITS ATTAINMENT) 

HOW TO KNOW HIGHER WORLDS

Theosophy. An Introduction to the Supersensible Knowledge of the World and the Destination of Man

An Outline of Esoteric Science, formerly Occult Science, An Outline

Christianity as Mystical Fact