Populate drop down fields according to other fields in Drupal 7 Let's say I have a content type car with content fields brand and model. Now I want to populate the field model according to the value of brand that the user will select. So for example if have:


BMW

series 1
series 3

mercedes

a class
b class



So if a user chooses BMW as a brand the model field should be populated with series 1 and series 3.
May be hierarchical select is what you are looking for.

Use one taxonomy field with hierarchy to store brands and models. hierarchical_select module will create nice widget for choosing them.