Failure analysis of fiber optic cables, components and devices from manufacturing operations, installation and field deployment has been important in reliability assurance for fiber optic communications networks. In this overview presentation, we consider optical fiber transmission failures in fiber optic cables and optical transmission impairments accompanied by mechanical failures in cable assemblies and interconnecting devices. In either case, failure analyses involve detailed characterization of optical and/or mechanical performance under varying environmental conditions such as temperature and humidity. In the case of optical transmission failures of fiber optic cables, we show that the environmental history of the cables and the thermomechanical response of buffer tube materials are of critical importance in understanding low-temperature transmission loss due to thermally-induced fiber microbending. In optical transmission impairments accompanied by fiber mechanical failures of cable assemblies and interconnecting devices, the environmental history along with manufacturing practices used in the production of cable assemblies determine the performance and reliability in the field. For cable assemblies with fiber mechanical failures, fiber break source analysis (fractography) has many challenges in the analysis of fiber breaks where fiber fracture surfaces are readily accessible. However, it has been practically impossible to perform break source analyses in cases where fiber fracture surfaces are not accessible within cables and interconnecting devices. Thus, in this presentation, we review a series of failure analyses performed to identify the cause(s) of high insertion loss and reflectance failures of cable assemblies. An essential component of these failure analyses was the development of new methods for accessing fracture surfaces of broken fibers within connectors. These new methods involve chemical and thermal treatments to preserve all features of fracture surfaces and, therefore, evidence of failure origins.