I was reading [this question](https://stackoverflow.com/q/2903430/1882077) when I noticed a curious comment underneath:

> 
> not sure what the question is: you can use VB.NET and C# projects in one solution (though I wouldn't recommend doing so).
> 
> 
> 

I do this quite a bit, as we have legacy VB.Net code, and new code is written in C#. Is this really not recommended? Why not?
['https://Stackoverflow.com/questions/15706564', 'https://Stackoverflow.com', 'https://Stackoverflow.com/users/969613/']
The only reason that it wouldn't be recommended is consistency. Most developers prefer to deal with a single language when working on an application. Having a single language also means that your developers only need to know a single language rather than knowing both VB.NET and C# (even though the two are extremely similar).

If you need to mix legacy VB.NET and C#, there's no reason not to.
Why would you want to do that? If you have legacy code what you want to use, you keep that code in its own components, you don't mix it with the new code. It is not recommended because it does not promote "Clean Code". It can lead you to have a solution that is difficult to read and maintain.