Abstract The observation of resonant-state products in nuclear reactions by measurements of coincidences between decay partners is proposed as a general spectroscopic tool for nuclear physics. The importance of the kinematic confinement of final-state resonant systems to a cone in the laboratory system is discussed and applied to various resonant particles. Several nuclear reactions leading to such resonant particles as final-state products are suggested and a brief discussion of the general nature of resonant-particle spectroscopic studies is presented.