Useful ISOs for cleaning companies include ISO 45001, ISO 9001 and ISO 14001. ISO 45001 is the Standard for occupational health & safety and can help you to keep your employees safe, even when working on other sites. ISO 9001 is the Standard for quality and can demonstrate to your clients that you put their satisfaction at the heart of your business. You may also want to think about ISO 14001, the Standard for environmental management, because it can raise the green credentials of your company.