Shepherd's allows you to track the citation history of a court case. When you "Shepherdize" a case, you will see all of the other cases that have cited that case, and if they treated the case favorably or unfavorably. This is how you can tell if the law in your case is still considered "good law" or if it has been overturned or challenged by other cases.
Shepherd's is only available through LexisNexis, and has been around for more than 100 years. It is a very common and important process in legal research.
To start, make sure you have the citation for your case. Then, find the case in LexisNexis Academic -- use the option to "Look Up a Legal Case" at the bottom of the homepage, or from the top of the page select "Search by Subject or Topic". Under the "Legal" heading, select "Federal and State Cases".
Once you have searched for and located your case, you will see a small symbol at the top of the case page. This symbol indicates how you should proceed with using the case law -- positively, with caution, or stop and evaluate. The legend of symbols will be found at the bottom of the case page.
To Shepherdize the case, on the right side of the screen, a drop down menu that says "More like this" is found next to the words "Next Steps". Click on the drop down menu and select "Shepherdize". The next screen will show you all of the cases that have cited your case, and how they have treated it.
For a visual overview of this process, see the video below.