The lunar module's interior was as different from that of other manned spacecraft as its exterior. It took two years to design. To design a vehicle that would fly and also be a home on the moon required some very special features. To be able to provide the trip to the moon some of the things that needed to be considered were visibility and equipment for rendezvous and docking. To be able to provide a home while on the moon the design needed to consider environmental control for living, an easy means for leaving and reentering while on the moon, and the capability to operate in a low-gravity or no-gravity environment.

It was decided that the crew would stand up when flying and landing the lunar module because seats would be too heavy and restrictive for the bulky space suits. Since the flight would be brief, and the g loads moderate (one g during powered flight and about five on landing), it was decided that human legs could handle the landing impact.

Grumman was told by NASA that above all, the spacecraft must be designed so that the hover and touchdown could be flown manually and so that no single failure of the controls or displays could cause a mission abort.

William F. Rector was the lunar module project officer. He felt that the astronauts should be part of the lunar module design process because they were going to fly it. Astronauts Scott Carpenter, Charles Conrad, and Donn F. Eisele drew the lunar module as their special assignment. These astronauts were both engineers and test pilots and so they were able to offer suggestions and to look over the plans as they developed. Charles Conrad probably worked more on the vehicle's basic design than any other pilot. One innovation which Grumman favored, and which Conrad was instrumental in getting incorporated, was electroluminescent lighting. This type of lighting made the controls easier to see and kept the lighting for each of the panels at the same level. This was so effective in the lunar module that it was used in the command module as well.