Question: Like the title says:

I have a `DateTime start` and a `DateTime stop`

Now i want to compare these with a `List<DateTime> dates`

I just wanto check if the list `dates` is between `start` and `stop`

`if(dates.all(..... >= start && <= stop)) {
. do something
}`

Answer: 
The pseudo-code in your question is not far from the working code you're looking for.

Using LINQ's [All()](http://msdn.microsoft.com/en-us/library/bb548541.aspx) method:

```
if (dates.All(date => date >= start && date <= stop)) {
    // Do something.
}

```
Sort the list.
Check if the first item in the list is >= start date and last item in the list <= end date