Recently, I switched to a new PC. For my Silverlight projects, I downloaded and then installed Silverlight SDK 5.from Download Microsoft® Silverlight® 5 SDK from Official Microsoft Download Center . Then I opened my Silverlight project, but could not find ESRI.ArcGIS.Client.dll, ... as references. Since I haven't touch the project for several years, I could not remember what else I should do in order to add the related references. Thanks if you can hint me.