Food security is a major global concern. It has insidious effects on the health and development of young children and consequently, adults. The paper assesses the food security status and its key determinants for the rural households of the high rainfall zone (HRZ) of Murang’a, semi–arid lands (SALs) of Kitui and arid lands (ALs) of Isiolo in Kenya. A three stage sampling technique was used for respondents (384) selection. Data collected were: demographics, livelihood strategies, food security and livelihood assets. Descriptive and Inferential Statistical methods and descriptive Content Analysis were used. Inferential statistics analytical methods were: ANOVA, PMC, T-test and regression. Overall food insecurity was 48%, but this varied across the agro–ecological zones, with the most affected being the SALs of Kitui at 81% to ALs of Isiolo at 75%. The most food secure was the HRZ of Murang’a at 77%. Food security was significantly different [F (2, 381) = 41.01, P<0.05] across the agro–ecological zones. Livelihood assets accounted for 37.2% (R2=0.372) of the variability in household food security in the study areas. Specifically, livelihood assets accounted for 28.9%, 37.6% and 42.5% of the variation in household food security in the ALs of Isiolo, SALs of Kitui and HRZ of Murang’a respectively. The overall main determinants for household food security were: natural [t(384)= 9.364, p=.000], physical [t(384)=3.523, P=.000] and financial [t(384)=3.120, P<0.05] capitals. The main determinants for the specific agro–ecological zones were: HRZ of Murang’a; natural [t(228)=8.412, p=.012], physical [(228) =3.778, P=.000] and financial [t(228) =2.784, P=0.002] capitals, SALs of Kitui; financial [t(100) =7.67, P=.000], natural [t(100) = 10.294, P<0.05], social [t(100)=3.42, P<.05] capitals and ALs–Isiolo; natural [t(56)=3.626, P=.000], financial [t(56) = 2.798, P<0.05] and human [t(56) =3.181, P<0.05] capitals. Contextualization of interventions on the determinants found to have significant on food security is necessary in addressing the perennial food insecurity in the study areas. Policies that facilitate food to be within reach and affordable at all times are worth promoting for improved security.