You do not have to work with an external consultant, but many companies use them to gain expertise and advice.  B Lab manages a training programme for consultants (called B Leaders), who are sustainable development professionals trained with the tools and expertise required to guide companies along the entire length of the B Corp certification process.  Working with B Leaders ensures you stay on track with the BIA that corresponds to you, successfully negotiate the difficult parts of the assessment, and correctly choose how to demonstrate your business impact model, should this be required.  We see a lot of companies start the BIA enthusiastically and determinedly, unfortunately only to falter after a few weeks. This requires implementing fully-fledged project management within the organisation and mastering HR, legal, environmental impact, etc. A professional can save you a lot of time and increase your chances of success. We have observed several advantages of using a B Leader: You can put in place a project management system that defines a timeline and identifies the resources to be used in-house (whether or not you decide to use a B Leader, allocating the right resources at the right time is definitely an advantage) You can negotiate the BIA with ease and efficiency (define your HR and organisational scope, understand the concepts, avoid biases linked to the vocabulary, etc.) You can mobilise your teams and support them, at their pace, so that they also manage their time and your resources as efficiently as possible. You will get an outside view of your operations and your impact. Sometimes we go round in circles because we are blinkered. Being challenged, hearing about the experiences of other companies in your sector, can be an opportunity to take stock and have a rethink.