Over the past two decades, numerous new hadrons have been observed in the charmonium and bottomonium energy regions. Many of these states reside near meson-antimeson thresholds and therefore can be considered as potential candidates for meson molecules. In this talk, I will discuss how to decipher the nature of such states from experimental line shapes and lattice QCD simulations. An overview of the effective-field-theory approach for analysing the near-threshold states will be presented. Some applications, e.g., to the recently discovered doubly charm Tcc(3875)+ state will be discussed.