This is stuff ive done lots of times before but my mind is just blanking at the moment, i will try and give a simple overview of my current situation. I currently have 3 tables as shown below: Office > id, name Person > id, name Office_Personnel > office_id, person_id I then have a model for Person (id, name) and Office, however the Office model contains personnel information: public class Office { int Id {get;set;} string Name {get;set;} ICollection<Person> Personnel {get;set;} } Mapping person is easy, but now im a bit stumped as to why office wont map properly. I chose to use a set when I was mapping the Personnel as there shouldn't be any duplicates, however it doesn't seem to work as I would expect... <set name="Personnel" table="office_personnel" cascade="all"> <key column="office_id" /> <one-to-many class="Person"/> </set> Now one thing that strikes me as odd is that there is no indication as to what person should be binding to (person_id). It keeps trying to find *office_id* column within the Person table. I'm sure this is just some simple problem and im being an idiot, but any help would be great! On a side note, I was weighing up if I should even bother having a middle man table, as I could directly put an Office_Id column within the Person table, but im not 100% sure if in my real project the Person class could be in multiple Offices further down the line...