Environmental Stress Screening (ESS) is a series of tests conducted under environmental stresses to expose weak parts and defects in workmanship so they may be corrected. It’s designed to remove latent part and manufacturing process defects through the application of environmental stimuli (e.g., random vibration, thermal cycling) prior to fielding equipment. 
Random vibration and thermal cycling have proven to be the most effective screens for precipitating defects in electronic equipment. An equally important and inseparable aspect of the screening process is the item’s electrical testing that is done as part of the screening process is the item’s electrical testing that is done as part of the screen, to detect and properly identify the defects that have been precipitated to failure. 
Contrary to popular belief, ESS does not increase the inherent reliability of a system. The inherent reliability of a system is driven primarily by the design, and ESS is one tool used to minimize the potential for adverse effects introduced by production. There are three phases in the development of an ESS program: 
- ESS Planning: Identify the equipment to be screened, develop quantitative goals for the ESS program, and describe initial screens.
- ESS Implementation: Identify the organizational elements that will be responsible for conducting the screening activity and the Data Collection, Analysis and Corrective Action System (DCACAS) to be used for documenting failures.
- ESS Monitoring: Continuously monitor the screening process to ensure that it is both technically and financially effective.
Several guide books can be referenced: 
- DoD Reliability Availability and Maintainability (RAM) Guide, Chapter 5.5.5
- Environmental Stress Screening (ESS) of Electronic Equipment, MIL-HDBK-344A, August 16, 1993.
- Environmental Stress Screening (ESS) Process for Electronic Equipment, MIL-HDBK-2164A, June 19, 1996.
- Management and Technical Guidelines for the ESS Process, Institute of Environmental Sciences and Technology, February 2000
AcqLinks and References:
-  DoD Reliability Availability and Maintainability (RAM) Guide, Chapter 5
-  Mil-HDBK 189 – Reliability Growth Management, 10 Sept 09
- Outdated: MIL-STD-785 “Reliability Program for System and Equipment Development & Production” – 15 Sep 80