The Rise and Fall of Star Faring Civilizations in Our Own Galaxy - Speculation, based on the Drake Equation, regarding the existence and composition of alien civilizations.

Life Extraterrestrial: Life on Other Planets in the Solar System - Curriculum framework for comparing Earth to other planets with regard to life.

Cosmic Ancestry: The Modern Version of Panspermia - The Cosmic Ancestry hypothesis - about which this site has a large amount of information - treats all of evolution, not just the origin of life on Earth, as due to interaction with cosmic microorganisms.

The Planetary Society - A nonprofit organization devoted to the exploration of the solar system and the search for extraterrestrial life.

Strato's Space Center - An overview of the possibilities of extraterrestrial life within the solar system.

The Search for Extraterrestrial Life - Scientific American article by Carl Sagan. Provides a layman's overview to the building blocks of life and current efforts in the search for extraterrestrial life.

The Drake Equation - Describes the famous formula for estimating the number and character of alien civilizations within the galaxy. Includes an online form that calculates your numbers.

We Are Not Alone - Essay on the probability of extraterrestrial life.