A high strength steel sheet, the high strength steel sheet having a yield-point elongation (YP-EL) of 1% or greater and a tensile strength of 980 MPa or greater, the high strength steel sheet having a chemical composition containing, in mass%, C: 0.030% or greater and 0.250% or less, Si: 2.00% or less, Mn: 3.10% or greater and 6.00% or less, P: 0.100% or less, S: 0.0200% or less, N: 0.0100% or less, and Al: 1.200% or less, optionally, in mass%, at least one element selected from Ti: 0.200% or less, Nb: 0.200% or less, V: 0.500% or less, W: 0.500% or less, B: 0.0050% or less, Ni: 1.000% or less, Cr: 1.000% or less, Mo: 1.000% or less, Cu: 1.000% or less, Sn: 0.200% or less, Sb: 0.200% or less, Ta: 0.100% or less, Zr: 0.0050% or less, Ca: 0.0050% or less, Mg: 0.0050% or less, and REM: 0.0050% or less, with a balance of Fe and incidental impurities, and the high strength steel sheet having a microstructure in which ferrite is present in an area fraction of 30.0% or greater and less than 80.0%, martensite is present in an area fraction of 3.0% or greater and 30.0% or less, bainite is present in an area fraction of 0% or greater and 3.0% or less, retained austenite is present in a volume fraction of 12.0% or greater, a ratio of the number of retained austenite grains adjoining a retained austenite grain having a different crystal orientation to the total number of retained austenite grains is 0.60 or greater, the ferrite has an average grain size of μm or less, the retained austenite has an average grain size of 2.0 μm or less, and a value obtained by dividing a Mn content in mass% of the retained austenite by a Mn content in mass% of steel is 1.50 or greater, wherein a value obtained by dividing a volume fraction Vya by a volume fraction Vyb is 0.40 or greater, where the volume fraction Vya is a volume fraction of retained austenite in a fractured portion of a tensile test specimen after a warm tensile test at 150°C, and the volume fraction Vyb is a volume fraction of retained austenite before the warm tensile test at 150°C, and wherein the YP-EL, the TS, the area fractions of ferrite, martensite and bainite, the volume fraction of retained austenite, the ratio of the number of retained austenite grains and the average grain size of ferrite and retained austenite are measured utilizing the methods described in the description. the high strength steel sheet having a chemical composition containing, in mass%, C: 0.030% or greater and 0.250% or less, Si: 2.00% or less, Mn: 3.10% or greater and 6.00% or less, P: 0.100% or less, S: 0.0200% or less, N: 0.0100% or less, and Al: 1.200% or less, Ti: 0.200% or less, Nb: 0.200% or less, V: 0.500% or less, W: 0.500% or less, B: 0.0050% or less, Ni: 1.000% or less, Cr: 1.000% or less, Mo: 1.000% or less, Cu: 1.000% or less, Sn: 0.200% or less, Sb: 0.200% or less, Ta: 0.100% or less, Zr: 0.0050% or less, Ca: 0.0050% or less, Mg: 0.0050% or less, and REM: 0.0050% or less, with a balance of Fe and incidental impurities, and the high strength steel sheet having a microstructure in which ferrite is present in an area fraction of 30.0% or greater and less than 80.0%, martensite is present in an area fraction of 3.0% or greater and 30.0% or less, bainite is present in an area fraction of 0% or greater and 3.0% or less, retained austenite is present in a volume fraction of 12.0% or greater, a ratio of the number of retained austenite grains adjoining a retained austenite grain having a different crystal orientation to the total number of retained austenite grains is 0.60 or greater, the ferrite has an average grain size of μm or less, the retained austenite has an average grain size of 2.0 μm or less, and a value obtained by dividing a Mn content in mass% of the retained austenite by a Mn content in mass% of steel is 1.50 or greater, wherein a value obtained by dividing a volume fraction Vya by a volume fraction Vyb is 0.40 or greater, where the volume fraction Vya is a volume fraction of retained austenite in a fractured portion of a tensile test specimen after a warm tensile test at 150°C, and the volume fraction Vyb is a volume fraction of retained austenite before the warm tensile test at 150°C, and wherein the YP-EL, the TS, the area fractions of ferrite, martensite and bainite, the volume fraction of retained austenite, the ratio of the number of retained austenite grains and the average grain size of ferrite and retained austenite are measured utilizing the methods described in the description.