The duties and responsibilities of a Billing Specialist include sending invoices and account updates to clients, receiving, sorting, and tracking incoming payments, addressing and resolving client questions and issues relating to invoices, and providing regular, accurate reports of billing data. Billing is the process of issuing invoices and collecting payments from customers. It is a crucial part of any business, ensuring companies can cover costs and generate revenue. In its most basic form, billing involves sending an invoice to customers who must then make a payment within a specific timeframe.