A complaints sheet, complaints book[1]​ or complaints book is a document through which a consumer can record a complaint regarding a good or service that he or she has purchased. More specifically, the official complaint form is one approved by a public administration in a specific format, imposing obligations on establishments open to the public regarding its possession and processing.

In the complaint, the consumer can present his complaints by expressly mentioning a specific claim (for example, refund of the price of a good), or simply state what he considers an infringement. In that case, the claim sent to the administration would have the character of a complaint.

In the event that there is a specific claim by the client, the administration can act as a mediator of the conflict between the two parties. The competent administration receives the claim form and opens proceedings to verify the reported complaint and may mediate the conflict, even referring the parties involved to an arbitration procedure. This arbitration procedure, if accepted by the parties, would be a substitute for ordinary jurisdiction"), which in any other case would always remain at the disposal of the consumer.

In the business environment, conflicts can also occur between consumers and businessmen, with the type of claims being very diverse.

The most frequent, related to the quality of the product, are usually due to being in poor condition, not meeting the promised standard, not being what was expected or other reasons. There may also be complaints about the service, due to delays or non-compliance with dates, not being sufficiently satisfactory or not complying with what was agreed in the contract, among others. In relation to the price, the reasons for which complaints are usually due to errors in the application of the price in the order or invoice, the inclusion of VAT. not anticipated by the client, finding the product at another price from another supplier or a misinterpretation by the client. Regarding technical complaints, they may concern a general malfunction or a specific part, too many breakdowns or excessive time dedicated to maintenance. On the other hand, complaints about staff attention usually occur because the client does not feel adequately cared for.

In the event that a consumer files a complaint or claim at the municipal Consumer Information Office, the consumer must receive information about their rights.

In Spain, there are not only traditional routes, in some specific sectors there are other administrative routes where you can complain. These are the sectors that have some other competent Administrative channel to manage claims: