Spren are creatures of nature. With the exception of Shinovar, where there are no spren, they have a common presence all over Roshar and tend to be ignored, or remain unseen. Spren are not fully understood. They take different shapes and forms, appearing around certain events, ideas, or abnormalities. Some types of spren have taken on " ... cognitive ideals or concepts which have [in turn] taken on literal personification over time."
According to Jasnah ...
|“||" ... spren are elements of the Cognitive Realm that have leaked into the physical world. They're concepts that have gained a fragment of sentience, perhaps because of human intervention."
"Spren are those ideas - the ideas of collective human experience - somehow come alive."
"Shadesmar is where that first happens, and it is their place. Though we created it, they shaped it. They live there; they rule there, within their own cities."
"Spren are wild in their variety. Some are as clever as humans and create cities. Others are like fish and simply swim in the currents."
"The spren are not always forthcoming. In some cases, they do not know. In others, they do not trust me because of our ancient betrayal."
"They tell me of it ... but they won't say what it was. We broke an oath, and in so doing offended them greatly. I think some of them may have died, though how a concept can die, I do not know."
"When once humans and spren bonded, the results were women who danced in the skies and men who could destroy the stones with a touch."
According to Brandon ...
|“||"The general fundamental rules that create spren are cosmere-wide. Spren are pieces of Investiture, usually pieces of Investiture that come straight from one of the Shards of Adonalsium, split off in some way, that because of human or other sapient creatures thinking about it or interacting with the power, the power starts to take on a life of its own. The power develops personality and comes alive, so to speak. And this can happen on any planet - in any place where there is Investiture. So it could happen on any planet in the cosmere with significant amounts of free Investiture. The places you’ve seen this happen most commonly are Sel and Roshar. You haven’t seen it on Scadrial, and you’ve seen little kind of hints of it on Nalthis, but not quite. But it’s possible for it to happen anywhere. Seons and spren are basically the same thing with different powers kind of pushing them, pushing growth out of them - that said, the non-sapient spren, the spren that are not quite as ... . They’re not going to stand up and talk to you. But those all existed ... not all, but most of them existed on Roshar before the Shattering of Adonalsium."||”|
–Brandon Sanderson
According to Dalinar ...
Spren should be extreme; they were forces of nature.
–Dalinar's thoughts ... 
Origins of Spren
Some of the many spren found on modern Roshar were created by Honor and Cultivation at some point before the Desolations started, by Splintering themselves. After Odium killed Tanavast, Honor's bearer, he Splintered Honor further, creating the many diverse spren found on Roshar. Some spren are also apparently the result of Investiture left behind by Adonalsium himself.
According to Pattern, when the Knights Radiant existed, spren were everything ... in everything, yet not their selves. He informs Shallan that none who had experienced the Nahel bond were alive then; they were dead, meaning mindless ... because a force cannot truly be destroyed. Further, he states that these old ones are now patterns in nature, like unborn Cryptics, and that they cannot be restored, because this has been tried but does not work. He supposes that if their Knights still lived, something could be done.
|“||"Spren with minds were less plentiful then, and the majorities of several spren peoples were all bonded. There were very few survivors. The one you call the Stormfather lived. Some others. The rest, thousands of us, were killed when the event happened. You call it the Recreance."||”|
|“||" ... the old spren have four genders instead of two."*||”|
–Syl to Kaladin
Spren can be very elusive and even the most common types may refuse to appear. Axies the Collector finds this to be particularly frustrating. Spren are typically amorphous and often change in size, luminosity, and shape. Whether they actually manifest physically remains in question. However, Geranid, along with her husband Ashir, found that a spren will stay the same size after being measured if that measurement is recorded. This rule holds true even if the person performing the measurement does not know whether or not the measurement is being recorded. The cause for this is unknown.
Spren can also be killed ... by those to whom they are bonded should each their bonded individuals break his/her vows. Regarding this bond, the synergy between the behavior and the relationship is one of constructive interference - but it goes both ways. The desired behavior reinforces the budding relationship, and the strengthening relationship reinforces the desired behavior, and it's just not possible to have one without the other. But "constructive interference" can be a two-edged sword - when the results are undesirable, it's also known as a vicious cycle.
Spren live in Shadesmar, the Cognitive Realm. There, they have different forms than those in which they appear on Roshar. They are more complex beings that are part of an entire ecosystem of their own, rather than the partial manifestations as they appear in the physical world.
When Adolin asks Syl how it even works, she tells him that it's certainly less messy than his method. Further, she tells him that spren are made of power, that they are bits of gods. And, that there are places where that power coalesces, and parts start to be aware. Additionally, she says that it doesn't happen often, that it's rare, and that most spren will go hundreds of years without doing it.
When Kaladin asks Syl whether most of the spren in Celebrant are hundreds of years old, she tells him that most of them are, or older. But, she says, that aging isn't the same with spren. Like time isn't. That they don't learn as fast, or change much, without a bond.
- Main article: Nahel bond
Some spren choose just what human with which to bond; this depends on the spren's type. The choices of certain other spren are made by counsel; Wyndle, Lift's spren, was placed with Lift by such a counsel known as The Ring. It's a cultural difference. Some spren are free-spirited; others are more organized.
They have their own society in Shadesmar, and they have their own culture, hierarchy and politics. For example, the Cryptics (liespren) and the honorspren seem to be two groups of spren nobility, and they have a strong mutual dislike for each other. They also seem to have differing views on whether or not spren should be bonding with humans.
Whilst many spren appear to do nothing but gather around whatever they are named after, some people think that the spren cause the things they're named after rather than the other way around. For instance, many believe that rotspren cause infection in a wound, as opposed to gathering as a sign that there is an infection present. Human perception has a lot to do with why spren act like they do.
However, spren do appear to be significant relative to the various powers of the Knights Radiant orders, which appear to be available to people who are bonded by a spren in the way that Syl is bonded with Kaladin.
|“||" ... all spren are, in a sense, virtually the same individual. There's harmony in that."||”|
–Syl to Kaladin
|“||"Spren appear when something changes - when fear appears or when it begins to rain. They are the heart of change, and therefore the heart of all things."||”|
|“||"So they're all spren," he said. "Shardblades."
Syl grew solemn.
"Dead spren," Kaladin added.
"Dead," Syl agreed. "Then they live again a little when someone summons them, syncing a heartbeat to their essence."
"How can something be 'a little' alive?"
"We're spren," Syl said. "We're forces. You can't kill us completely. Just ... sort of."
"That's perfectly clear."
"It's perfectly clear to us," Syl said. "You're the strange ones. Break a rock, and it's still there. Break a spren, and she's still there. Sort of. Break a person, and something leaves. Something changes. What's left is just meat. You're weird." 
Types of Spren
- Main article: Spren Types
Spren come in many different varieties, each associated with and named for their own phenomenon. Most spren are non-sentient, however, some could become sentient and there are some that already are, for example Kaladin's honorspren. It's been theorized, that the process of becoming sentient might be linked to the Nahel bond.
They also have their own names ... names that don't necessarily relate to the name that Roshar inhabitants give them.
- Ashspren (a Dustbringerspren)
- Cryptic (a liespren, or Lightweaverspren)
- Cultivationspren (an Edgedancerspren)
- Cusicesh the Protector (unknown type)
- Glys (a Truthwatcherspren)
- Highspren (a Skybreakerspren)
- Honorspren (a Windrunnerspren)
- Inkspren (an Elsecallerspren)
- Ivory (an inkspren, or Elsecallerspren)
- Liespren (a Cryptic, or Lightweaverspren)
- Lightspren (a Willshaperspren)
- Nightwatcher (a Cultivationspren)
- Pattern (a liespren, or Cryptic, or Lightweaverspren)
- Phendorana (an honorspren, or Windrunnerspren)
- Rua (an honorspren, or Windrunnerspren)
- Spark (an ashspren, or Dustbringerspren)
- Stormfather (a Bondsmithspren)
- Sylphrena (a honorspren, or Windrunnerspren)
- Timbre (a lightspren, or Willshaperspren)
- Ua'pam (a peakspren, or Stonewardspren)
- Winnow (a highspren, or Skybreakerspren)
- Wyndle (a Cultivationspren, or Edgedancerspren)
The chasmfiendspren, santhidspren and skyeelspren seem to be connected. They may have some kind of anti-gravitational effect. However, spren have seemed to be drawn to things, rather than causing things. Are there some spren that do one, some do the other, and some do both? Or are these "anti-gravity spren" more closely related to the bonding spren (i.e., do they grant a limited Surgebinding to these creatures)? How much intelligence is actually required for a bond like that?
*So, singers also have four genders (plus one) instead of two. Might these be related, since the Parshendi were residents of Roshar long before humans were?
Q&A with Brandon
Q. In your books, readers see a lot of really interesting and diverse world elements that make places and cultures really come to life. What are some of the world elements you’ve had the most fun creating, and what do you like best about them?
A. I'd say that the spren on Roshar have been my favorite so far - they are so different, but also so RIGHT. They have a mythological fae-feel to them, but also fit into the cosmere arcanum just perfectly. I also like writing them.
Q. Is it true that humans can bond to multiple spren?
A. They can theoretically bond to multiple spren.
Q. How do spren choose what human they'll bond with?
A. Well, it depends on the spren type. There's some spren that choose on their own, while there's other spren where it's done by committee. Wyndle, Lift's spren, was placed with Lift by a committee. It's a culture difference. Some are free spirited, others more organized.
Q. Are spren bound to Roshar or can they travel to other worlds? Could they do so if they were bound to someone that traveled to other worlds?
A. RAFO! Excellent question, though.
Q. The phenomenon that creates spren. Is that Roshar-specific or is that a general effect?
A: Well, yes and no. The general fundamental rules that create spren are cosmere-wide. Spren are pieces of Investiture, usually pieces of Investiture that come straight from one of the Shards of Adonalsium, split off in some way, that because of human or other sapient creatures thinking about it or interacting with the power, the power starts to take on a life of its own. The power develops personality and comes alive, so to speak. And this can happen on any pla - in any place where there is Investiture. So it could happen on any planet in the cosmere with significant amounts of free Investiture. The places you’ve seen this happen most commonly are Sel and Roshar. You haven’t seen it on Scadrial, and you’ve seen little kind of hints of it on Nalthis, but not quite. But it’s possible for it to happen anywhere. Seons and spren are basically the same thing with different powers kind of pushing them, pushing growth out of them - that said, the non-sapient spren, the spren that are not quite as ... . They’re not going to stand up and talk to you. But those all existed ... not all, but most of them existed on Roshar before the Shattering of Adonalsium.
Spren are investiture which is alive.
- Cognitive ideals ...
- Words of Radiance, 1. Santhid
- Oathbringer, 4. Oaths
- Spren are part of Honor
- Spren and Seons
- Spren are Splinters
- Words of Radiance, 75. True Glory
- Oathbringer, 7. A Watcher At The Rim
- The Way of Kings, Inter5.
- Physical manifestation ...
- The Way of Kings, Inter8.
- The Way of Kings, 14. Payday
- Can spren die?
- Oathbringer, 99. Reachers
- Spren live in Shadesmar
- Spren exist in the Cognitive Realm
- Oathbringer, 108. Honor's Path
- Oathbringer, 102. Celebrant
- Words of Radiance, Inter9.
- Human perception ...
- The Way of Kings, 60. That Which We Cannot Have
- The Way of Kings, 17. A Bloody, Red Sunset
- The Way of Kings, 37. Sides
- Words of Radiance, 87. The Riddens
- Spren becoming sentient ...
- Shinto ...
- Spren are drawn in ...
- Creating spren ...
- Bonding multiple spren?
- Choosing a human ...
- Worldhopping spren?
- JordanCon 2016