State departments of transportation and other bridge owners are faced with significant challenges in addressing the Nation's highway bridge preservation and replacement needs. More than 25 percent of the Nation's 600,000 bridges are rated as structurally deficient or functionally obsolete. More than 30 percent of existing bridges have exceeded their 50-year theoretical design life and are in need of various levels of repairs, rehabilitation, or replacement. This issue is exacerbated by increasing travel demands, limited funding, and increasing costs of labor and materials. These circumstances have caused most bridge owners to become more reactive than proactive in their approach to managing and addressing their bridge program needs. Bridge stewards and owners need to become, inevitably, more strategic by adopting and implementing systematic processes for bridge preservation as an integral component of their overall management of bridge assets. A successful bridge program seeks a balanced approach to preservation and replacement. Focusing only on replacing deficient bridges while ignoring preservation needs will be inefficient and cost-prohibitive in the long term. Adopting a "worst first" approach to managing bridge assets may also yield ineffective results that allows bridges in good condition to deteriorate into the deficient category which generally is associated with higher costs and other challenges. The objective of a good bridge preservation program is to employ cost effective strategies and actions to maximize the useful life of bridges. Applying this appropriate bridge preservation treatments and activities at the appropriate time can extend bridge useful life at lower lifetime cost. This guide provides bridge related definitions and corresponding commentaries, as well as the framework for a systematic approach to a preventive maintenance program. The goal is to provide guidance on bridge preservation.