This paper reports the organolanthanide-catalyzed intramolecular hydroamination/cyclization of amine-tethered unactivated 1,2-disubstituted alkenes to afford the corresponding mono- and disubstituted pyrrolidines and piperidines using coordinatively unsaturated complexes of the type (η5-Me5C5)2LnCH(TMS)2 (Ln = La, Sm), [Me2Si(η5-Me4C5) 2]SmCH(TMS)2, and [Me2Si(η 5-Me4C5)(tBuN)]LnE(TMS)2 (Ln = Sm, Y, Yb, Lu; E = N, CH) as precatalysts. [Me2Si(η 5-Me4C5)(tBuN)]LnE(TMS)2 mediates intramolecular hydroamination/cyclization of sterically demanding amino-olefins to afford disubstituted pyrrolidines in high diastereoselectivity (trans/cis = 16/1) and good to excellent yield. In addition, chiral C 1-symmetric organolanthanide catalysts of the type [Me 2Si(OHF)(CpR*)]LnN(TMS)2 (OHF = η 5-octahydrofluorenyl; Cp = η5-C5H 3; R* = (-)-menthyl; Ln = Sm, Y), and [Me2Si(η 5-Me4C5)(CpR*)]SmN(TMS)2 (Cp = η5-H3C5; R* = (-)-menthyl) mediate asymmetric intramolecular hydroamination/cyclization of amines bearing internal olefins and afford chiral 2-substituted piperidine and pyrrolidine in enantioselectivities as high as 84:16 er at 60 °C. The substrate of the structure NH2CH2CMe2CH2CH=CH(CH 2)2CH=CH2 is regiospecifically bicyclized by [Me2Si(η5-Me4C5)( tBuN)]LnE(TMS)2 to the corresponding indolizidine skeleton in good yield and high diastereoselectivity. Thermolysis of (η 5-Me5C5)2LaCH(TMS)2 in cyclohexane-d12 at 120 °C rapidly releases CH 2(SiMe3)2 and leads to possible formation of fulvene (η6-Me4C5CH2-) species. The thermolysis product readily reverts to active catalysts upon protonolysis by substrate and exhibits the same catalytic activity as the (η 5,η1-Me5C5) 2LaCH(TMS)2 precatalyst at 120 °C in the cyclization of cis-2,2-dimethylhept-5-enylamine. Catalytically-active lanthanide-amido complexes (η5-Me5C5) 2La(NHR)(NH2R)n and [Me2Si(η 5-Me4C5)(tBuN)]Sm(NHR)(NH 2R)n are shown to be thermally robust species.