Continuous monitoring techniques are needed for assurance that the stack gases of hazardous and municipal waste incinerators do not emit unacceptable levels of dangerous compounds. The development of suitable on‐line “real‐time” monitors may help answer current public concerns regarding the safety of thermal processing methods and may simplify the permitting process for new facilities. Recent research is reviewed which suggests that resonance ionization mass spectrometry is capable of real‐time monitoring of wide classes of toxic molecules at the part‐per‐billion level against complex backgrounds of interferant species. Recent advances in laser technology promise to make on‐line repetitive multispecies monitoring of hazardous emissions a practical reality.