The National Dairy Herd Fertility Project (renamed the InCalf Project) consists of two large, prospective observational studies conducted in commercial dairy herds from 4 Australian states. The project aims to identify factors associated with variation in reproductive performance between cows and herds. The larger of the two studies included over 33,000 cows and 168 herds. The database has undergone extensive error checking and correction resulting in high quality data. Large variations in reproductive performance were observed between cows and herds, indicating that there are important risk factors for reproductive performance and that cows and herds are exposed to varying combinations of these risk factors. Models for several reproductive outcomes were constructed using multivariable stepwise logistic regression. No significant associations were detected between any measures of cow genetic merit and 6 week in-calf rate. Neither milk volume nor protein yield were significantly associated with 6 week in-calf rate. A weak negative association was detected between fat yield in the first 120 days of lactation and 6 week in-calf rate. However, differences in estimated 6-week in-calf rate between moderate and high producing groups (2 to 5 percentage points) were small when contrasted against the 63 percentage point range in performance observed between herds (23% to 86%).