This paper is a discussion of old and newly placed time capsules, with a view to providing guidelines for retrieving and burying them. The use of copper sheet and tinplate on 19th century time capsules fosters an acidic interior environment which can damage contents. Contents, particularly acidic paper, also affect the microclimate. Growth of microorganisms is another possibility. Guidelines for careful inspection of exterior and opening are provided. Contents should be allowed to equilibrate to ambient relative humidity for several hours after opening. A conservator should be contacted regarding the care of items found in the capsule. For constructing a new time capsule, stainless steel is considered by far the best material. Options for sealing capsules are discussed, including o-rings, wing nuts, and welding. Too little is known of the long-term durability of plastics to recommend their use. The author evaluates the contents of most time capsule he has opened as unexciting. He suggests means of choosing artifacts that are evocative of our times when capsules are placed. The interior should exclude oxygen and water as much as possible. Silica gel crystals will help dry the interior. There are a number of means for removing oxygen. Individual objects should be packed separately. Placement within the building should be planned carefully.