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Abstract: This work undertakes, we believe for the first time, a study of the chemistry of alkyl halides in Na0 treated zeolites. It concludes that untreated zeolites do nucleophilic chemistry to the degree that the host is electron donating. It concludes that Na0 treated zeolites do a mixture of nucleophilic, electron-transfer, and free radical chemistry. Zeolites NaX and NaY and their Na0 treated forms (Na0/NaX and Na0/NaY) were exposed to linear1-haloalkanes (Cl, Br, I). NaY is inert in all cases. Framework alkoxy and halide ion are formed in NaX from the Br- and I-alkanes in an electrophilic attack of framework oxygen on the alkyl halide, while the leaving of the halide ion is assisted by the electrostatic attraction of the NaX site III or III′ Na ions. In Na0NaX and Na0/NaY direct reaction of Na0 with the alkyl bromide or iodide yields a larger alkane and halide ion, probably via a free radical mechanism involving two Na0 and two alkyl halides. The NaX–alkyl chloride chemistry includes exclusively or partly dehydrohalogenation, yielding 1-alkenes and chloride ion. Na0/NaX or Na0/NaY–alkyl chloride dehydrohalogenation chemistry yields chloride with 2-alkenes in low yield and alkanes in higher yields. 1-Chloropropane yields the framework propoxy and propene from NaX and yields these products plus other olefins from Na0/NaX. Overall the yields and reactivity fall into a pattern of Lewis basicity increasing in the order NaY