What is Mass Assignment? Assigning multiple attributes of a record with params received from the application within a single query. For example,{:user => {:first_name => "FirstName", :last_name => "LastName", :role => "admin"}} So while creating a new record in User table, we specify as => User.create(params[:user]) In the above query, rails gives the freedom for one-to-one mapping of params attributes with model-record attributes. Lets say, we don't explicitly specify as User.create(:first_name => params[:user][:first_name], :last_name => params[:user][:last_name].......). Such assignments