Organic room temperature phosphorescence (RTP) is the radiative emission of triplet excitons, which occurs with a phosphorescence lifetime, t ph , ranging from microseconds to milliseconds. In the past decade, the development and study of organic RTP materials have gained increasing attention due to their potential in applications across diverse fields such as optoelectronics, lasers, sensing, imaging, data storage, and X-ray scintillators. To date, a plethora of design motifs have been proposed, mainly based on the modulation of intramolecular and/or intermolecular interactions. These RTP design principles are primarily based on improving the intersystem crossing (ISC) efficiency and/or suppressing the non-radiative and oxygen quenching deactivation of the triplet excitons. For example, ISC efficiency has been shown to be enhanced via the incorporation of heavy atoms, the breaking of conjugation, and the introduction of a charge-transfer (CT) bridge motif and resonance linkage (intramolecular modulation). Also, matrix rigidification, molecular aggregation, and polymerization have each been demonstrated to suppress the non-radiative decay of triplet excitons (intermolecular interactions) for achieving efficient RTP systems.