Another Join Problem

[Victor Subervi]

Hi;
I get the following error:

*SQL query:*

SELECT ID, Item
FROM products
JOIN categories ON categories.ID = products.Category
LIMIT 0 , 30;

 *MySQL said:*
 #1052 - Column 'ID' in field list is ambiguous

Please note the error is about ambiguity. "products" has an ID field and so
does "categories". If I run the statement taking out the "ID" from the
select, it runs. So, where is the ambiguity??
TIA,
V