<p>Recombinant protein expression in plant cells is a desired biotechnological process that involves introducing foreign genes into host cells and producing the corresponding proteins. Hairy roots, which are produced from the infection of plant tissues by a soil-borne bacterium, <i>Rhizobium rhizogenes</i>, are great hosts for this purpose. The hairy root system offers advantages such as ease of protein extraction, low production costs, no risk of human pathogens, and scalability in bioreactors. However, the challenges of this system include low and variable expression levels, transgene instability, and complex gene expression regulation. This review provides an overview of the status and prospects of hairy root technology for recombinant protein expression, with a focus on species such <i>Nicotiana</i> species, the most commonly used host plants. The review also discusses the main factors affecting hairy root transformation, recombinant protein expression, and recovery, as well as the strategies to improve them.</p>