# Company codes

Source: https://developer.avalara.com/avatax-for-ap/ief9609549543193/

# Company codes

Learn about company codes, their role in AvaTax, and how to manage them effectively.

AvaTax supports both simple, single-company structures and more complex business structures. Specifically, it supports one-level deep child companies of a parent company. A child company can either be a separate filing entity with its own configuration or inherit taxability settings from the parent company.

Each AvaTax account can include as many child companies as needed to reflect its business structure. Each company is identified by a unique `companyCode` value in the [CreateTransaction](https://developer.avalara.com/api-reference/avatax/rest/v2/methods/Transactions/CreateTransaction/) API. The `companyCode` determines the tax rules that apply to a transaction.

If you don't include the `companyCode` when running a transaction, AvaTax automatically assumes that you want to use the default company. Every AvaTax account has a default company, but because a complex business can have dozens of companies, we recommend always including the `companyCode` value.

As a connector developer, most of your users will have a simple company structure. But whether simple or complex, consider providing a dropdown list of companies in your UI and automatically displaying (and highlighting) the company with the `isDefault` flag set to `true`. To retrieve the list of available companies for your UI, call the [QueryCompanies](https://developer.avalara.com/api-reference/avatax/rest/v2/methods/Transactions/CreateTransaction/) API.