Many steps in the control of gene expression are dependent on RNA-binding proteins, most of which are bi-functional, in as much as they both bind to RNA and interact with other protein partners in a functional complex. A powerful approach to study the functional properties of these proteins in vivo, independently of their RNA-binding ability, is to attach or tether them to specifically engineered reporter mRNAs whose fate can be easily followed. Two tethering systems have been mainly used in eukaryotic cells, namely the MS2 coat protein system and the lambda N-B box system. In this review, we firstly describe several studies in which these tethering systems have been used and provide an overview of these applications. We next describe the major features of these two systems, and, finally, we highlight a number of points that should be considered when designing experiments using this approach.