Display records found in 1 table but not the other

I have 2 tables, let's pretend they are called Table1 and Table2. A column found in both tables is called "MyNumber".

I need to write my select statement to show all records in Table1, but only if the record isn't in Table2.

If the result for "MyNumber" is in Table1 and Table2, I don't want it to display in my query. I only want the records from Table1, that are not found in Table2 to display.

Can someone help?

I am not sure if I should use Exist, or NOT IN... or...

I'm not sure what would be the most efficient method.

Thank you.