Most of the books I write are parts of a series.
Some of them are set in the same place but each book has its own self contained story and HEA for that couple. The Chase Brothers series is this way, as is the Petal, Georgia series, my Brown Family and Delicious books for instance. These books will have a cast of characters and a world that builds with each new book as those characters all experience new things. So you could read book four of the Brown Family novels (Never Enough) and you’d get a book about a guy who finds out he’s got a twelve year old he never knew he existed. It’s a love story between Adrian and his son, and a romance between Adrian and Miles’ mother Gillian. If you dig in a layer and have read the other books, you also know Adrian’s brother and sister and one of his friends have also found their HEA and all their stories have built a foundation in Never Enough as well. But you could absolutely understand Never Enough without having read the other books (though the experience is deeper if you have)
I also write in terms of multiple book story arcs within a series. Each book as a self contained HEA but there’s a multiple book meta-story happening. Most frequently these books are my paranormal romances or my futuristics. Bound By Magick has had four separate HEAs but there’s one big story that’s been building since book one. The first four Cascadia Wolves books are also like that, and the first two de La Vega books were also one larger story as well as a complete romance per book. My Federation Chronicles are also based on one, sweeping world with big giant politics, an impending war, etc. While you can enjoy the romances in each, every single book builds into the next with one large story. You won’t understand what’s going on in the world if you pick up book five and you haven’t read the others. Sure, you can read the romance in it and that isn’t hard to understand, but you won’t know about the class underpinnings of this huge world and so your experience won’t be the same, or complete.
Sometimes I write in a meta world and connect series across it. For instance – my Cascadia Wolves, de La Vega Cats and my Bound By Magick series are all set in the same world. I’ve had characters from the various series show up in books from the other series – I LOVE this. You don’t need to have read the de La Vega cats books to understand Going Under when Mia (Gibson’s mate from Beneath the Skin) is the pilot the witches use to fly Molly and her PR tour around. It’s a fun easter egg for fans of the series and creates some fun threads, but it’s not necessary to have read the other series for understanding. I’ve just begun a new series crossover mini series that starts with UNCONDITIONAL and will be a story arc over at least the next book. This is the story from my Bound By Magic books, but told from the perspective of the shifters. There will be a fully contained HEA per book, but an overarching storyline that takes these characters through a devastating world event and how they deal with the aftermath.
Writing a series enables me to create a big world that is fleshed out. It connects characters, places and stories and each new book in a series makes things bigger and more three dimensional. It gives me new ways to write, new things to try, new ways to approach stories and my characters. I love to write series and I’m so thrilled my actual job is to keep on doing so!