在一个Visual Studio实例中可以有多个项目。VS解决方案的重点是将你想要使用的所有项目集中在一个地方，所以你不能在一个实例中有多个解决方案。你必须分别打开每个溶液。

这就是Visual Studio的设计方式:一个解决方案，一个Visual Studio (VS)实例。

除了在一个VS实例中的解决方案之间切换之外，你还可以打开另一个VS实例，并用该实例打开你的另一个解决方案。正如你所说，解决方案旁边是“项目”。在一个解决方案中可以有多个项目，因此可以同时查看多个项目。

我想到了两种方法……

Open another visual studio window and open the second solution in it. It would be preferable to add your existing projects to one solution, just right click and add existing project and navigate to the project file(csproj). .... e.g. C:\Users\User\Documents\Visual Studio 2012\Projects\MySqlWindowsFormsApplication1\MySql Windows Forms Project1\MySql Windows Forms Project1.csproj ....In this second way you might want to setup multiple start up projects i.e. for people with client-server apps or apps with dependencies. ....To do this Select the solution then GoTo: Project>>Properties>>Startup Project>> Select Multiple Startup projects and set actions to Start. When you debug, the selected as start will run. For interest sake you could open another multiple solution windows to view different projects at the same time. http://www.schwammysays.net/visual-studio-2012-tip-multiple-solution-explorers/

MAC users - this issue was winding me up, as its not possible to open two different Visual Studio instances at the same time. Ive found a solution that works fine, though its a little unorthodox : get the latest beta testing version, which will install alongside your normal VS install in a separate sandbox (it does this automatically). You can then run both versions side by side, which is enough for what I needed - to be able to examine one project for structure, code etc., while doing the actual coding I need to do in the 'current' VS install instance.

右键单击Visual Studio图标，然后在Windows 8底部的上下文工具栏中选择“新建窗口”。一个新的Visual Studio实例将启动，然后您可以打开第二个项目。

如果你有两个独立的解，那么你不能在同一个VS实例中同时查看它们。但是，您可以在它们之间打开多个VS和制表符实例。

另一种选择是将项目从一个解决方案导入到另一个解决方案中，从而将所有项目放入一个解决方案中。你可以按照以下步骤来做:

在“解决方案资源管理器”中，选择要导入项目的解决方案。右键单击，并从上下文菜单中选择Add->Existing Project。 在文件选择器中，找到想要导入的项目文件(它将以. xxproj结尾，其中XX是您正在使用的语言)。 点击打开，瞧!项目已导入。