Background. There has been sustained and growing interest in characterizing the net energy impact of
information and communication technology (ICT), which results from indirect effects offsetting (or
amplifying) the energy directly consumed by ICT equipment. These indirect effects may be either
positive or negative, and there is considerable disagreement as to the direction of this sign as well as the
effect magnitude. Literature in this area ranges from studies focused on a single service (such as
e-commerce versus traditional retail) to macroeconomic studies attempting to characterize the overall
impact of ICT. Methods.Wereview the literature on the indirect energy effect of ICT found via Google
Scholar, our own research, and input from other researchers in the field. The various studies are linked
to an effect taxonomy, which is synthesized from several different hierarchies present in the literature.
References are further grouped according to ICT service (e.g., e-commerce, telework) and
summarized by scope, method, and quantitative and qualitative findings. Review results. Uncertainty
persists in understanding the net energy effects of ICT. Results of indirect energy effect studies are
highly sensitive to scoping decisions and assumptions made by the analyst. Uncertainty increases as
the impact scope broadens, due to complex and interconnected effects. However, there is general
agreement that ICT has large energy savings potential, but that the realization of this potential is highly
dependent on deployment details and user behavior. Discussion. While the overall net effect of ICT is
likely to remain unknown, this review suggests several guidelines for improving research quality in
this area, including increased data collection, enhancing traditional modeling studies with sensitivity
analysis, greater care in scoping, less confidence in characterizing aggregate impacts, more effort on
understanding user behavior, and more contextual integration across the different levels of the effect
taxonomy.