Driven by the increasingly overwhelming environmental issues caused by the widespread application of traditional toxic corrosion inhibitors, eco-friendly inhibitors have attracted strong attention over the past decades. Green inhibitors are produced from cheap and renewable sources and simultaneously offer high inhibition efficiency and low or even zero environmental impact. Herewith, we review recent advances in the field and introduce state-of-the-art methods to validate the inhibitory effects on steel corrosion. Advanced techniques such as weight loss, electrochemical impedance, and potentiodynamic polarization techniques provide ample evidence that green inhibitors are very effective in retarding steel corrosion. We critically examine the mechanisms of corrosion inhibition and relate to the available experimental data. The abundance of π-electrons of multiple bonds and heteroatoms in the form of polar functional groups leads to the active adsorption of the inhibitor’s molecules on the steel surface. This article further discusses the adsorption and inhibition mechanisms and the efficiencies of various groups (organic and inorganic) of green corrosion inhibitors for steels in aggressive acid environments, in particular, hydrochloric (HCl) and sulfuric (H2SO4) acids. The future prospects in this multidisciplinary field are formulated and associated with the global challenges of clean energy and manufacturing.