Objective— To determine whether biomarkers of oxidized lipoproteins are genetically determined. Lipoprotein(a) (Lp[a]) is a heritable risk factor and carrier of oxidized phospholipids (OxPL). Approach and Results— We measured oxidized phospholipids on apolipoprotein B–containing lipoproteins (OxPL-apoB), Lp(a), IgG, and IgM autoantibodies to malondialdehyde-modified low-density lipoprotein, copper oxidized low-density lipoprotein, and apoB-immune complexes in 386 monozygotic and dizygotic twins to estimate trait heritability ( h ² ) and determine specific genetic effects among traits. A genome-wide linkage study followed by genetic association was performed. The h ² (scale: 0–1) for Lp(a) was 0.91±0.01 and for OxPL-apoB 0.87±0.02, which were higher than physiological, inflammatory, or lipid traits. h ² of IgM malondialdehyde-modified low-density lipoprotein, copper oxidized low-density lipoprotein, and apoB-immune complexes were 0.69±0.04, 0.67±0.05, and 0.80±0.03, respectively, and for IgG malondialdehyde-modified low-density lipoprotein, copper oxidized low-density lipoprotein, and apoB-immune complexes 0.62±0.05, 0.52±0.06, and 0.53±0.06, respectively. There was an inverse correlation between the major apo(a) isoform and OxPL-apoB ( R =−0.49; P <0.001) and Lp(a) ( R =−0.48; P <0.001) and OxPL-apoB was modestly correlated with Lp(a) (ρ=0.57; P <0.0001). The correlation in major apo(a) isoform size was concordant ( R =1.0; P <0.001) among monozygotic twins but not dizygotic twins ( R =0.40; P =0.055). Lp(a) and OxPL-apoB shared genetic codetermination (genetic covariance, ρG=0.774±0.032; P =1.09×10 ⁻³⁸ ), although not environmental determination (environmental covariance, ρE=0.081±0.15; P =0.15). In contrast, Lp(a) shared environmental but not genetic codetermination with autoantibodies to malondialdehyde-modified low-density lipoprotein and copper oxidized low-density lipoprotein, and apoB-immune complexes. Sib-pair genetic linkage of the Lp(a) trait revealed that single nucleotide polymorphism rs10455872 was significantly associated with OxPL-apoB after adjusting for Lp(a). Conclusions— OxPL-apoB and other biomarkers of oxidized lipoproteins are highly heritable cardiovascular risk factors that suggest novel genetic origins of atherothrombosis.