VB.NET and C# Interoperability

Analogy categoryAnalogies

Why VB.NET and C# Can Work Together

VB.NET and C# both compile down to the same Common Intermediate Language (CIL) and run on the same Common Language Runtime (CLR), which means a class written in VB.NET is, at the metadata level, indistinguishable from an equivalent class written in C#. This shared runtime is what allows a VB.NET class library to be referenced from a C# console app, or a C# Web API project to consume a VB.NET business-logic assembly, with no translation layer required. The CLR only cares about the compiled assembly's type metadata, not the source language that produced it.

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Cricket analogy: Think of the CLR like the ICC's standard pitch dimensions and ball specifications: whether a bowler trained in Mumbai or Melbourne, the delivery still has to conform to the same rules, so a VB.NET assembly and a C# assembly both 'play by' identical CIL rules and can share the same match.

Compiling to a Common Intermediate Language

When you build a VB.NET project, vbc.exe (the Visual Basic compiler) emits CIL and metadata into a .dll or .exe, exactly as csc.exe does for C#. Tools like ildasm.exe or a decompiler such as ILSpy will show that a VB.NET Public Sub DoWork() and a C# public void DoWork() produce nearly identical IL opcodes. This is why a C# project can add a project reference (or a compiled DLL reference) to a VB.NET class library, call its public members directly with IntelliSense support, and get full type-checking at compile time -- there is no interop marshaling involved, unlike calling into unmanaged C++.

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Cricket analogy: Whether a scorecard is compiled from a scorer using the traditional book method or a digital scoring app, both ultimately produce the same standardized scorecard format that the match referee and broadcasters read identically, just as vbc.exe and csc.exe both emit the same CIL format.

vbnet

' MathHelpers.vb -- compiled into MathHelpers.dll
Public Class MathHelpers
    Public Shared Function Square(ByVal n As Integer) As Integer
        Return n * n
    End Function
End Class

csharp

// Program.cs -- a C# console app referencing MathHelpers.dll
using System;

class Program
{
    static void Main()
    {
        int result = MathHelpers.Square(9);
        Console.WriteLine(result); // 81, called directly, no marshaling needed
    }
}

Mixed-Language Solutions in Visual Studio

Visual Studio fully supports a single solution containing both VB.NET and C# projects side by side, with project references crossing the language boundary in either direction. A common real-world pattern is a legacy VB.NET WinForms front end sitting on top of a newer C# class library that implements business rules, or the reverse, a C# ASP.NET Core API calling into a VB.NET data-access layer inherited from an older system. NuGet packages, MSBuild targets, and the debugger all work uniformly across the mixed solution, so you can step from a C# breakpoint directly into VB.NET code and back without leaving the debugger.

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Cricket analogy: An IPL franchise can field a squad with players contracted from different domestic boards (say, a Mumbai player and an Adelaide Strikers player) under one unified team sheet, just as one Visual Studio solution fields VB.NET and C# projects under one unified build.

In Visual Studio's Solution Explorer, cross-language project references work exactly like same-language references: right-click the referencing project, choose 'Add > Project Reference', and select the target project regardless of whether it's VB.NET or C#. No special interop wizard is needed.

Language Feature Differences That Affect Interop

Despite sharing the CLR, VB.NET and C# are not fully symmetric in the features they expose, and a few of these differences leak across interop boundaries. VB.NET supports optional parameters with default values in a way that predates C#'s equivalent, and VB.NET's ParamArray maps to C#'s params keyword, but both are visible to callers in the other language via IntelliSense. More subtly, VB.NET is case-insensitive by design (a legacy of classic Visual Basic), while C# is case-sensitive, so a VB.NET project cannot declare two members that differ only by case, but a C# library it references can -- and VB.NET code consuming that C# library must reference the exact casing the C# author used, since VB.NET's own compiler still enforces its own case-insensitive rule only within VB.NET source, not on external assemblies.

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Cricket analogy: The DRS (Decision Review System) rules differ slightly between formats -- Test cricket allows unlimited reviews for umpire's call overturns in some boards' rules while T20 caps reviews strictly -- so a team moving between formats must adapt, just as code moving between VB.NET and C# must adapt to each language's feature quirks.

Because VB.NET is case-insensitive, it cannot directly reference two members of a C# type that differ only in case (e.g., a C# interface with both Id and ID properties will cause a compile error in consuming VB.NET code with an 'ambiguous' or duplicate-name error). Rename or alias the conflicting member in the C# source if VB.NET consumers are expected.

Case Sensitivity and Naming Conflicts

Case sensitivity also affects how you name your own VB.NET members when a C# consumer will use them: since VB.NET won't stop you from writing Function getValue() while a base class in C# defines GetValue(), you can accidentally create a shadowing or overload conflict that only clearly surfaces when the C# consumer's compiler treats the two as distinct members. Best practice on mixed teams is to adopt and enforce the same PascalCase / camelCase conventions used by the .NET Framework Design Guidelines in both languages, so casing differences never become a source of interop bugs, and to run a linter (like StyleCop for C# and equivalent VB analyzers) as part of CI to catch this early.

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Cricket analogy: A team that lets bowlers choose their own field placements without coordinating with the captain risks two fielders covering the same spot and leaving a gap elsewhere, just as uncoordinated naming between VB.NET and C# teams risks accidental member conflicts.

VB.NET and C# both compile to CIL and run on the same CLR, so assemblies interoperate directly without marshaling.
Visual Studio solutions can freely mix VB.NET and C# projects with cross-language project references and unified debugging.
vbc.exe and csc.exe produce nearly identical IL for equivalent code, which is why decompilers show similar output regardless of source language.
VB.NET is case-insensitive while C# is case-sensitive, which can cause ambiguous-member errors when VB.NET consumes a C# type with case-only distinct members.
Language feature differences (default parameters, ParamArray vs params, event handling syntax) are usually visible and usable cross-language via IntelliSense.
Adopting shared naming conventions (.NET Framework Design Guidelines) across a mixed-language team prevents casing-related interop bugs.
No special interop wizard or adapter layer is required for VB.NET-to-C# references, unlike calling into unmanaged or COM code.