In short: a mix of internal and external experts, including key people that couldn’t participate in the whole sprint. 

It is recommended to bring in experts for interviews at the start of a Design Sprint to better understand the topic and get a first round of inspiration. 

When I recruit people to be interviewed as experts, I try to have a good mix:

• Internal expert: people from within the company who are very knowledgeable on the topic or on past projects that are similar. 

• Internal strong voice: people who are very critical internally or that, from a “ political perspective,” it’s important that you’ve listened to (maybe these people didn’t want to participate in the sprint or aren’t the right fit but still have important information to share).

• External local expert: experts outside of the direct industry but that know the topic well and the local culture. 

• External international expert: experts outside of the direct industry and who come from another country. It’s always a nice “ wow” moment when you bring someone that isn’t local into the mix.

The choice of the expert is therefore not just a matter of knowledge but also a good political play (by choosing internal strong voices) and motivation boost (by having international experts).