The concept of "summer series" is one which has long been of some interest to me (it's something I probably first became aware of in the late 80s). For as long as I can remember, and surely starting long before my time, seasons for TV shows, in America, have been thought of generally as beginning in fall and running through the end of spring. Summer has, traditionally, been associated with reruns. Of course, as more and more people have gotten cable or satellite, the way they've thought of TV has changed, to some extent, but as far as broadcast networks are concerned, the thinking has remained essentially the same. And for the most part, it's accurate. However, I also cannot recall a time when there has not been original programming during the summer months. (This generally includes all of June through September, in spite of those months technically including the end of spring and beginning of fall, respectively. It's also worth noting that some series may premiere in winter or spring, rather than fall or summer; these I will usually not consider summer series. Although if something premieres before June, but the bulk of the season is in summer, I will.) Summer programming can come in the form of specials or TV movies & miniseries, though of course such things can also air at any time of year (and can be rerun in the summer, just like regular series). Original programming can come in the form of sports (though I don't watch such things, with rare exceptions). It can come in the form of reality shows (though I don't watch such things). It can come in the form of new episodes of cancelled series being "burned off." It can come in the form of series that split their TV seasons into halves airing in different seasons of the year, of which summer may be one. (This happens a lot on cable, and I'm not even going to list such shows, here. *)
It is possible that some shows I have thought of as summer series were actually... shows that failed to make it to the fall schedule. And then there are series that, in spite of premiering in summer, were always intended (or hoped) to continue in the fall, but never did. Certainly some things that I consider summer series, such as "CBS Summer Playhouse," weren't even failed series, but failed pilots. (I knew that, when the series aired, but while the pilots themselves may not have been meant for summer, the series itself became an anthology, of a sort, and it even had "Summer" right in the title. So obviously it was a summer series.) But there are some series that are never intended, by networks or creators (as far as I know), for anything but summer. (Some may be limited series intended to run for a single summer, and some may have multiple seasons over multiple summers.) And I get annoyed if anyone sees any sort of stigma attached to this, much as it can bother me if people belittle direct-to-video (or DVD) movies. True, in both cases, summer or video, the reason can be failure, but that doesn't mean it's always failure. Some such things can be really great. And in rare cases, a summer series may end up becoming a regular series. The example that always comes to mind, for me, is "Northern Exposure." But I should add, there have been plenty of series, over the years, that if I look back now, I may not remember at all what time of year they originally aired. So... I'll rely on the internet to tell me. (Note that this page is just for shows I personally have seen or at least heard of. I'm sure there were many summer series before my time, or even within my time, things I couldn't have seen because- for the most part- I had no access to any network but CBS until the mid-90s. No doubt I'll forget some shows I have seen. And even now, there are some summer series I don't list here simply because I'm not interested in them, in the same way that there are many fall series I'm not interested in.)
Similarly-themed web pages:
Metacritic: The Best Summer TV Series of All Time
(I've seen other sites that discuss summer series before I started this page, but right now I can only find this one. Maybe sometime I'll add some other links, though.)
The Days and Nights of Molly Dodd, on NBC
IMDb; TV.com; TV Tango; Wikipedia
I didn't actually get NBC at the time this aired, but the title is familiar to me, and I know my local CBS affiliate also aired some shows from other networks. So it's possible I saw a bit of this (or it could just be something I'd heard of). Either way, I remember nothing about it, now, including when it aired. But apparently, season one was May 21 to August 13, 1987. Season two was March 24 to June 29, 1988 (with another episode in April 1989). Apparently, after NBC cancelled it, Lifetime produced three more seasons, which also ran in summer (or spring).
CBS Summer Playhouse, on CBS
As I mentioned in the introduction, this was just a collection of various unrelated, unsold pilots. I don't suppose I saw much of it, or at least I don't remember much of it, but I'm sure it was of interest to me, while it was on. It aired from June 12 to September 19, 1987; June 21 to September 6, 1988; and June 20 to August 22, 1989.
The Jim Henson Hour, on NBC
This ran for just one season, from April 14 to July 30, 1989, so it's more of a spring and summer series. I don't remember for sure if I saw it or not, but I kinda think I did.
Doctor Doctor, on CBS
The first season was a mere six-episode run from June 12 to July 24, 1989, before beging picked up for two more full fall seasons.
Seinfeld, on NBC
Originally titled "The Seinfeld Chronicles," the first episode aired July 5, 1989; the remaining four episodes of the first season aired almost a year later, from May 31 to June 21, 1990. The second season aired from January to June of 1991. It wasn't until the third season that it became a regular fall series. But of course, we now think of it as one of the most successful sitcoms in recent history, if not one of the most successful sitcoms ever. (It ultimately ran for nine seasons.)
Northern Exposure, on CBS
The first season ran from July 12 to August 30, 1990. It did well enough that it got a second season in the spring of 1991, and a third season premiered that fall. It ultimately ran for six seasons, and became one of my personal favorite shows ever.
Wish You Were Here, on CBS
This ran from July 20 to August 24, 1990.
Sunday Dinner, on CBS
This ran from June 2 to July 7, 1991. It's one of the few shows on this page that I think was meant to last longer than the summer, but... it didn't.
Golden Years, on CBS
This ran from July 16 to August 22, 1991.
Morton & Hayes, on CBS
This ran from July 24 to August 28, 1991.
Mann & Machine, on NBC
This ran from April 5 to July 14, 1992, so it's more of a spring & summer series.
Grapevine, on CBS
This ran from June 15 to July 27, 1992.
Swan's Crossing, in syndication
This ran from June 29 to September 25, 1992. I wish it would've gotten a second season.
Freshman Dorm, on CBS
IMDb; TV.com; TV Tango; Wikipedia
This ran for just five episodes, from August 11 to September 9, 1992. I had completely forgotten it existed, until one day when I was looking for old shows online, and the title jumped out at me. I don't remember anything about it, but I'm sure I must have watched it, and probably enjoyed it. Mainly because Robyn Lively was in it, and I've always quite liked her. Anyway, probably it was meant to last longer than the summer, but it didn't. (And it was late summer, so maybe it was intended more as an early fall series.)
Route 66, on NBC
This ran for just four episodes, from June 8 to July 6, 1993.
Family Dog, on CBS
Amblin; IMDb; Retro Junk; TV.com; TV Tango; Wikipedia
This ran from June 23 to July 28, 1993. It seems to me I watched it at the time because Tim Burton was involved in making it, but now I don't remember anything specific about the show. I don't think it was as interesting as I'd hoped it would be.
Johnny Bago, on CBS
This ran from June 25 to August 18, 1993.
Danger Theatre, on FOX
This ran from July 11 to August 22, 1993.
Big Wave Dave's, on CBS
This ran from August 9 to September 13, 1993.
Muddling Through, on CBS
This ran (I think) from July 9 to September 7, 1994.
Hotel Malibu, on CBS
This ran from August 4 to September 8, 1994.
Roar, on FOX
This ran from July 14 to September 1, 1997.
Invasion America, on The WB
This ran from June 8 to July 7, 1998.
Mamimum Bob, on ABC
This ran from August 4 to September 15, 1998.
Baby Blues, on The WB
This ran from July 28 to August 24, 2000, before being cancelled. In 2002, the series reran on adult swim, along with five previously unaired episodes (which is probably when I first saw the show).
Witchblade, on TNT*
The first season ran from June 12 to August 21, 2001. The second ran from June 16 to August 26, 2002. (I wish it would've gotten another season, though.)
Night Visions, on FOX
This ran from July 12 to September 6, 2001. (A few other episodes later aired on Sci-Fi.)
Pepsi Smash, on The WB
The first season ran from July 16 to August 20, 2003. The second from May 27 to July 15, 2004. To be honest, I'm sure how much, if any I watched of this, but I must have at least been aware of it. It was basically a concert series, I guess. Dunno what else to say.
Summerland, on The WB
The first season ran from June 1 to August 17, 2004. The second from February 28 to July 18, 2005 (so it's more of a winter-summer series). The series had a definite summery feel to it, being set mainly at the beach.
The 4400, on USA Network*
The first season ran from July 11 to August 8, 2004. The second from June 5 to August 28, 2005. The third from June 11 to August 27, 2006. The fourth from June 17 to September 16, 2007. It should have gotten another season.
What It's Like Being Alone, on CBC
This ran from June 26 to September 18, 2006.
Nightmares & Dreamscapes, on TNT
This ran from July 12 to August 2, 2006.
Masters of Science Fiction, on ABC
This ran from August 4-25, 2007.
Fear Itself, on NBCC
This aired from June 5 to July 31, 2008.
The Middleman, on ABC Family*
This ran from June 16 to September 1, 2008. It should have gotten at least another season, dammit.
The Good Guys, on FOX
This initially had a summer run between May 19 and August 2, 2010. The first (and only) season got picked up to continue its run from September to December of that year, before being cancelled. So it's more of a late spring to early winter series.
Falling Skies, on TNT*
The first season ran from June 19 to August 7, 2011. The second from June 17 to August 19, 2012. The third from June 9 to August 4, 2013. The fourth from June 22 to August 31, 2014. The fifth from June 28 to August 30, 2015. (Unfortunately, so far I've only been able to see the first season.)
Sullivan & Son, on TBS*
The first season ran from July 19 to September 13, 2012. The second from June 13 to August 22, 2013. The third from June 24 to September 9, 2014.
Defiance, on Syfy*
The first season ran from April 15 to July 8, 2013, so it's actually more of a spring and summer series. The second from June 19 to August 28, 2014, so that's definitely summer. The third from June 12 to August 28, 2015.
Under the Dome, on CBS
The first season ran from June 24 to September 16, 2013. The second from June 30 to September 22, 2014. The third from June 25 to September 10, 2015. (But I chose not to watch past the first season.)
Camp, on NBC
This ran from July 10 to September 11, 2013.
Crossbones, on NBC
Amazon; A.V. Club; IMDb; NBC; TV.com; TV Tango; TV Tropes; Universal; Wikipedia
This ran from May 30 to August 2, 2014. However, I only watched the first two episodes. I wanted to like the show, but it was just too... I don't know. Weird, hard to follow, bland, whatever. John Malkovich was decent in a very unique take on Blackbeard, but otherwise the show didn't do much for me.
Extant, on CBS
The first season ran from July 9 to September 17, 2014. The second from July 1 to September 9, 2015. (I watched the first episode of season 2, but decided not to continue with the series after that.)
Wayward Pines, on FOX
The first season ran from May 14 to July 23, 2015. The second from May 25 to July 27, 2016.
Aquarius, on NBC
The first season ran from May 28 to August 22, 2015. The second from June 16 to September 10, 2016 (with a hiatus from mid-July to late August). But I stopped watching about halfway through season 2.
The Whispers, on ABC
This ran from June 1 to August 31, 2015.
Maya & Marty, on NBC
This ran from May 31 to July 12, 2016.
BrainDead, on CBS
This ran from June 13 to September 11, 2016.
Downward Dog, on ABC
This ran from May 17 to June 27, 2017.
Still Star-Crossed, on ABC
This ran from May 29 to July 29, 2017.
Salvation, on CBS
The first season ran from July 12 to September 20, 2017. The second from June 25 to September 17, 2018.
Midnight, Texas, on NBC
The first season ran from July 24 to September 18, 2017. But the second season aired in the fall of 2018.
Somewhere Between, on ABC
This ran from July 24 to September 19, 2017.
Elementary, on CBS
Normally this is a fall show, but season 6 aired in spring and summer, from April 30 to September 17, 2018. Season 7 ran from May 23 to August 15, 2019.
Reverie, on NBC
This ran from May 30 to August 8, 2018.
Take Two, on ABC
This ran from June 21 to September 13, 2018.
Trial & Error, on NBC
The first season aired in the spring of 2017, but the second ran from July 19 to August 23, 2018.
Agents of S.H.I.E.L.D., on ABC
Normally this is a fall show, but season 6 ran from May 10 to August 2, 2019.
The InBetween, on NBC
This ran from May 29 to August 14, 2019.
* Some cable series may air their entire seasons in summer- or mostly in summer, possibly starting in spring and/or ending in fall. This may be more coincidental than a specific plan for them to be "summer series," so I hesitate to include such shows here. Still, there's something to be said for technicalities, so I'll include some shows here even if I'm unsure about the actual intentions behind their scheduling.