Question: How to use Linq to find an item in a List of ProductCat where every ProductCat contains a List of Product.

I want to find the Product by ProductID.

Thanks

Answer: 
```
Product foundProduct = productCatList
            .SelectMany(list => list.Products)
            .Where(product => product.ProductID == whateverID)
            .SingleOrDefault()
```
Try this:

```
var results = from pc in myProductCats
              where pc.Products.Contains(ProductId)
              select pc;

```

You question is missing a lot of details. If you provide some code and the class structure I can provide a better answer.