The top-quark mass is a fundamental parameter of the Standard Model. We will motivate, why precision determinations of the top-quark mass are important in the upcoming high-energy run of the LHC and discuss the prerequisites in theory for the extraction of a well-defined mass parameter in a given renormalization scheme. We show that the top-quark's running mass in the MSbar scheme can be extracted with good precision at next-to-next-to-leading order in QCD and comment on methods to measure the top-quark mass parameter from comparisonto events with top-quark decay products.