AbstractCurrent information on the nature of the HR 2142 system is presented. The circumstellar material (CSM) including the mass flow toward and away from the mass-gaining B star has been studied from ∼ 100 IUESWP HIRES images obtained from 1979–95 and ground-based CCD data from KPNO acquired between 1985–2001. The strength and velocity behavior of the infall components to the UV Si ɪɪ lines seen during the primary shell phase (PSP) from Φ ∼ 0.70−0.98 resembles that observed in conventional Algol systems, but the inferred mass infall rate is too small to account for the massive Hα-emitting disk about the B primary. The cause for the mass outflow observed during the secondary shell phase (SSP) remains unknown, but a localized plasma that has been identified from phase-dependent variations in the emission component to Heɪ λ6678 may be part of the SSP phenomenon. Although the secondary remains undetected in the optical/IR spectral regions, UV data currently do not yield strong support for the presence of an O subdwarf as in the Φ Per system. HR 2142 may represent and earlier evolutionary stage of Φ Per and a possibly similar Be binary 59 Cyg.