Solar flare photons and energetic particles in space

I review the evolution of research on solar energetic particle events, beginning with Forbush's report of the ground level event of 1946, through the most recent observations of the Advanced Composition Explorer (ACE). The emphasis is on research that attempted to link solar flare electromagnetic emissions with the solar energetic particles (SEPs) observed in space following flares. The evolution of thought on this topic is traced from the initial paradigm in which SEPs were accelerated at the flare site (a δ-function in space and time) to the current two-class picture accommodating both impulsive acceleration at the flare site (small 3He-rich events) and prolonged acceleration at extended shocks driven by coronal mass ejections (large proton events). I conclude with some open questions; the most prominent of these concerns the relative contributions of the flare and shock acceleration processes to ''mixed'' or hybrid SEP events in which the distinguishing characteristics of the impulsive and gradual classes are blended