There are, I think,. six in this series, with the 6th out later this year, and the fifth winging its way to me from Amazon even as I type this.
   This is a brilliant series. I thoroughly enjoyed the first one and then, each time I started the next in the series, I thought, 'This one can't be as good as the last one.' But each one was.
   This is grand science fiction, rather like a modern-day Lensman series, beefing up the characterisation and, in an odd way, the realism. The interactions, the violence, the strange places... it's all brilliantly portrayed. If you are an SF buff - and possibly even if you aren't - you can't afford to miss the Expanse Series.