Caspase-8 signaling has proapoptotic, antinecroptotic, and proinflammatory signaling roles dependent on interaction with the adapter molecule FADD, oligomerization, and autocleavage. Previously, a Caspase-8 binding partner cFLIP
L
(FLIP, encoded by
Cflar
) was shown to prevent Caspase-8-dependent apoptosis, but permit Caspase-8-dependent inhibition of necroptosis. We sought to explore the role of FLIP in Caspase-8-dependent apoptosis induction, necroptosis inhibition, and inflammatory signaling inhibition in vitro and in vivo. We provide evidence that in mice with a mutation that prevents Caspase-8 oligomerization (
Casp8
FGLG/FGLG
), FLIP is necessary to inhibit necroptosis, promote apoptosis, regulate inflammation, and control lymphoproliferative disease. Unlike
Casp8
FGLG/FGLG
mice, Casp8
FGLG/FGLG
,Cflar
−/−
mice do not survive embryogenesis, but ablation of
Mlkl
, required for necroptosis, allows their survival to adulthood. Further, unlike
Casp8
FGLG/FGLG
,Mlkl
−/−
mice,
Casp8
FGLG/FGLG
,Cflar
−/−
,Mlkl
−/−
mice display lymphoproliferative disease. We analyzed apoptosis, necroptosis, and inflammatory signaling in
Casp8
FGLG/FGLG
mice with or without FLIP, gaining insights into the functions of the Caspase-8–FLIP heterodimer in vitro and in vivo.