Merging Data Sets with Full Outer Join

Hi All,

I would like to match some datasets. Both deliver variables AND cases 
which might or might not be present in all datasets:

This sequence

Kunden <- Kunden_2011 
Kunden <- merge(Kunden, Kunden_2012,
                by.x = "Debitor", by.y = "Debitor")

Kunden <- merge(Kunden, Kunden_2013,
                by.x = "Debitor", by.y = "Debitor")

Kunden <- merge(Kunden, Kunden_2014,
                by.x = "Debitor", by.y = "Debitor")

Kunden <- merge(Kunden, Kunden_2015,
                by.x = "Debitor", by.y = "Debitor")

delivers too few cases. So I guess it does an equi-join.

How can I join the datasets and keep the variables as well as the cases?

I am looking forward to your reply.

Kind regards

Georg