Recent years have been marked by a steady increase in decision support tools available for farmers. Likewise, the number of dairy herd management smartphone apps to support on-farm decision making has increased. The existing literature does not yet cover topics concerning the adoption of herd management smartphone apps or which specific functions of such apps are perceived as useful by dairy farmers. Thus, this study tries to close this research gap by providing results about the adoption and use of dairy herd management smartphone apps derived from an online survey conducted in 2018 with 280 German dairy farmers. Dairy farmers rate functions related to the observation of animal health, reproduction management and data gathering as most useful. By rating functions and not specific smartphone apps, the results are also of interest for dairy sectors and developers outside Germany. Our results show that in our sample 91% of the dairy farmers use a smartphone and 61% already use a herd management smartphone app. Moreover, 38% of the adopters use such an app on a daily basis. Technology adoption cannot solely be explained by economic reasoning, but also the beliefs about a technology play a crucial role in decision making. Thus, this study also sought to determine whether an extended Technology Acceptance Model could explain adoption and use of herd management smartphone apps applying partial least squares structural equation modelling. All hypotheses of the Technology Acceptance Model could be verified by this study. The key attitudinal components of the model are perceived ease of use and perceived usefulness, which both positively influence the intention to use herd management smartphone apps; this ultimately has a positive effect on the actual usage behavior. All in all, our model explained 33% of the variance in the actual use of herd management apps by German dairy farmers.