Energy savings in buildings as a goal in recently established buildings either residential or commercial has been nowadays paid much attention by many researchers, designers, and decision makers due to the need of reducing energy demand and global warming issues. This challenging goal is affected by several factors and roles which play important roles by which this goal is affected. Those factors in most cases are difficult to be treated by one method or design. Many proposed systems have been introduced for many years; their performance(s) have varied percentage(s) of achievement in terms of energy savings. In this setting, such a review paper could help much to draw a clear plan for researchers and buildings' designers to follow and get them directed to best and easiest systems. However, many review papers have been published which included many limitations, e.g., some review papers focused only on residential buildings. In general, there is a need to give an overview of reviewed papers with taking into account many factors and policies together with strategies applied. In this setting, it is understood that different designs have produced different levels of performance being achieved. In this review paper, Building Energy Savings Strategies and Systems (BE3S) are reviewed. Different points of views have been considered. For example, lighting control systems, buildings' retrofitting systems, and occupancy profiles related systems have been reviewed. This paper has also included different types of buildings on which strategies and systems have been applied. Reviewed papers are collected from top-tier journals published by very well-known publishers which are IEEE, Elsevier, Emerald, MDPI, and ACM. Indexing services adopted in this BE3S paper are Scopus and WOS. BE3S paper has only considered last 20 years providing a summary of recently designed strategies achieving semi-optimal performance(s) in terms of energy savings in buildings.