Energy Efficiency is a phrase that everyone talks about, but does everyone know the paths to achieve this efficiency? And are they all equally effective in their paths? In this book and as an expert in the field, I will try to shed some light on the paths to follow to preserve energy and consequently preserve our planet. To succeed in the work dedicated to energy efficiency, it is necessary to master all the tools to be used. This theme is in the minds of all, both individuals and country officials who constantly talk about it, but are they following the right paths to achieve their goals?