There has been interest in obtaining gas, dust, rocks, or soil samples from comets or nearby planets since the beginning of the space age in the 1950s. Flying a spacecraft to the destination and returning a sample in an Earth entry vehicle can accomplish this. The return spacecraft is called a sample return vehicle (SRV). Detailed studies of Martian samples can only be conducted on Earth. In the past decade there have been many studies investigating the feasibility and practicalities of sample return missions to Mars Samples collected on Mars will be sealed in a special capsule to prevent contamination. An ascent vehicle will launch the capsule from the surface of Mars. There are several ways to return the sample to Earth. One way is to use a Mars orbiter to capture the sample container and then begin an interplanetary trajectory to return the sample to Earth. This document is concerned with the Earth entry environment and the Earth entry portion of a sample return mission to the planet Mars. The document is intended to introduce the subject of atmospheric entry to engineers and scientists who do not have strong backgrounds in aerodynamics, aerothermodynamics and flight mechanics. Much of this material can be applied to entry into other planetary atmospheres by using the appropriate atmospheric and gravity models. This document discusses topics in atmospheric entry and presents examples in related disciplines.