In a general sense, when people talk about a keeper league, they are talking about a fantasy league where the league doesn't start fresh every season. Some players are carried over from the previous season to maintain continuity. At the extreme is a dynasty league, which usually refers to a league where all players are carried over from season to season.

Participating in a keeper league adds a new dimension to your strategy and gameplay. We've all been in a league where our draft just doesn't work out the way we had hoped, and it becomes clear pretty early that we aren't going to be able to compete in the current season. In a non-keeper, or redraft league, the best you can hope to do is to be a good sport, continue to manage your team, and hope that either your team performs a miracle or you can at least play the spoiler. In a keeper league, you instead switch your focus: if I can't win this season, how can I better position myself to win in the future? But within this general concept, there are many ways to implement a keeper league, and many questions a league must agree upon to form their rules.

This is typically the first question a new keeper league must address. If you keep too few players from season to season, then you defeat some of the purpose and strategy of having a keeper league to begin with. If you protect too many players, your league can become stagnant; if you finish in last place, but immediately notice that the top 50 players in the game won't be available to draft the following season, then the situation can be even more bleak than usual.

The simplest model, which many keeper leagues start with, is to pick a number league members are comfortable with, and all teams keep that many players each season. Again, there is no correct answer for this number; your league members need to discuss what aspects of the game strategy they want to stress and how much they want to encourage change and fluidity among the teams.

A more challenging model allows teams to protect a variable number of players. Such a league will often incorporate some notion of salary, such that you cannot necessarily just protect all the players you want. Without a salary of some sort, you would imagine that the winner of the league might very often just keep all their players, and be very difficult to beat the following season.

For many keeper leagues, the next step of evolution is to associate salaries with players, so that protecting one player instead of another has an impact on your strategy. As is usually the case with keeper leagues, there are many different ways to establish salaries. Here are some examples to spark discussion within your league:

• Player Tenure: A player can only be kept for a fixed number of seasons before they must be released back into the pool to be redrafted. This is a relatively simple model that starts to encourage player movement and parity in a league. For example, a rule that says, "All teams can protect up to five players, but no player can be kept more than three years in a row." is relatively simple to understand and implement.
• Team Tenure: A player has a salary that increases the longer he is kept on a team, and instead of being allowed to protect a fixed number of players, each team can protect a fixed number of years of service. For example, in a league that allows you to protect 10 years of service, you could protect 10 different players that were newly drafted in the current season, five players that had been newly drafted the previous year, one player that you loved and held for 10 years, or any combination, such as a player that had been held for five years, another player that had been held for three years, and two players that were newly drafted in the current season.
• Draft Position: The salary to sign a player is related to the position in which he is drafted. At the start of every season, a league typically has a draft to populate their entire roster, and for each player they chose to keep, they'll require one fewer draft pick. Which pick that is can associate value with the kept player. For example, many leagues say, "If you wish to protect a player you drafted this season, you must sacrifice a pick one round better than where you selected him. Each year after that, you must give up a pick one round higher still." So if I draft a player in the 5th round, and he turns out to be a solid player I'd like to keep, I could choose to keep him rather than having a 4th round pick the following year. If he continues to be valuable at that price, the following season I could give up a 3rd round pick to keep him, and so on. Such a league should have rules for possible scenarios like, "What happens when I give up a 1st round pick to keep a player, and then I want to keep him another year?" The answer might just be, "You can't, and you have to throw that player back into the pool to be drafted.", or the league might find some other way to penalize a team for further protecting such a player. Similarly, suppose during the season you trade for a player that another team drafted in the 4th round, and at the end of the season you conclude you'd like to protect that player as well as the player you selected in the 4th round. You would not necessarily have two 3rd round picks to forfeit for keeping both players, so there needs to be a rule defined to handle this case. It might be, "You can't do that. Pick one of them." Or it might be, "Then you'll have to give up a 2nd round pick for one of them instead." Or it might be anything else your league defines and agrees upon.
• Player Salary: Leagues that do an salary cap style draft have unique options related to keeper salaries, since every player that is drafted inherently has a salary associated with him. So a league could say, "If you wish to keep a player after he was selected in a salary cap draft, then you must increase his salary by $5 per year. The player is put on your roster, and your salary cap budget is reduced accordingly." And all these different possibilities and rules can interact; such a league might decide that the $5 increases will eventually make a player impractical to protect, or they might also implement a rule that says that no player can be kept for more than five straight years in any case.

In the end, every team needs to end up with the same number of players. So for every player they protect they need to forfeit one of their draft picks. But which pick they give up depends entirely on your rules. Some examples:

• All Teams Keep the Same Number of Players: For leagues where each team protects the same number of players, this can usually be resolved pretty simply. If every team protects X players, you can imagine that the first X rounds of your draft are just all the teams taking their keepers. Similarly, you could imagine that the last X rounds are just all the teams taking their keepers, and it would play out the same.
• Teams Keep Different Numbers of Players: For leagues where teams protect different numbers of players, this gets more complex. If I protect eight players, and you protect five players, there is a noteworthy difference between whether I use an extra three picks at the beginning of the draft or the end of the draft. Your league can decide which is more in the spirit of their goals. Putting those picks at the beginning of the draft puts a substantial salary on the kept players that isn't present if they are put at the end of the draft.
• Keepers Based on Draft Position: For leagues that value player salary in terms of a draft pick, then their keepers may effectively be scattered throughout the draft. Perhaps you and I each protect three players, but based on their past draft position I might give up my 1st, 5th, and 8th round picks to keep those players, whereas you might give up your 3rd, 12th, and 17th round picks to keep your players. Such a system is very powerful, but slightly more complicated to administer and maintain.
• Salary Cap Drafts: For salary cap drafts, there is no notion of draft position. Instead, each team will potentially be able to win a different number of players at draft to fill out their roster. If every team in your league protects the same number of players, then you don't necessarily need to adjust anyone's salary cap budget. But if your kept players have an associated salary, then that probably needs to get reflected in differing budgets per team, and if teams protect differing numbers of players you almost certainly want to have that reflected in budget. It has an important meaning if I protect six players and you protect three, but we both start with the same amount of money to fill out our rosters. Effectively, I'd be protecting three players as if I purchased them for $0.
• Draft Order: In just about any redraft league, the draft order proceeds in a snaking fashion; whoever picks first in the odd numbered rounds picks last in the even numbered rounds, and vice versa. In a keeper league, it is often interesting to revisit this assumption. The NFL, MLB, NBA, and NHL all give preferred draft position to teams that do poorly, in one way or another, in an effort to encourage parity. Your fantasy team may wish to do the same. Since the point of snaking the draft order is usually to not provide any undue advantage to teams that are all supposed to be drafting equally, you could instead say, "The team who finished last this year drafts first in every round next year, and the team who finished first drafts last in every round."

In addition to trading players in a keeper league, considering also trading draft picks, just as the major sports leagues do. A team in contention for this year's championship may wish to trade away a quality pick in the next draft for a player that is doing well in the present. And for the team that can't win this year, that may make perfect sense for them, particularly if that player has an excessive salary associated with protecting him. This is similar to professional sports teams that decide to rebuild and trade an expensive star for future draft picks or cheaper prospect players.

In a league where you are allowed to trade draft picks, it definitely will make the commissioner's life easier if every traded pick needs to have a corresponding pick traded in the other direction. Since all teams need to end up with the same number of players in the end, this helps maintain order. For example, imagine a league where I trade a player for your 1st round pick. Then at the end of the year, we both decide we hate our rosters so much we are protecting no players. At that point you would have no 1st round pick, I would have two 1st round picks, and we'd both have 1 pick in every other round. So if the draft proceeded in this fashion, I'd end up with an extra player, and you'd end up short a player. It simplifies things if instead we're forced to say, "I trade you the player and my last pick in the draft for your 1st round pick."

Many keeper leagues find that there can be strange dynamics when some teams are playing for the present while others are totally playing for the future. In actual major league sports, teams are beholden to their fans to play a competent, major league team. There is no parallel to this in fantasy, which can encourage a team to completely dump value. There are various types of rules that can help temper this imbalance:

• Salary Cap: Some leagues will implement some sort of in-season salary cap. This might limit the number of previous protected players any given team can have. For leagues that have salaries associated with players, this might limit the amount of player salary a team can accumulate via trade.
• Draft Order: Some leagues will put in measures to discourage giving up completely on the current season. Rather than simply reversing the draft order based on order of finish, a league might use a more complex system to establish the basic draft order. This is analogous to what the NBA does with their draft lottery, to ensure that doing horribly in the current season doesn't necessarily richly reward you for the following season.
• Trade Approval: Some leagues might use a trade approval system (manager votes, commissioner veto) that is intended to identify when a team has gone too far over the top and needs to continue to play a competent team in the present, rather than sacrificing entirely for the future.

We've presented a lot of scenarios, and a lot of questions to think about. It can seem overwhelming at first, but if you sort through it and come up with a set of rules your league is comfortable with, it can lead to a much deeper and more entertaining fantasy experience. It is important to come to clear agreement on what rules you are doing, and to document them fully to avoid misunderstandings and frustration once you start playing, but if you come up with a solid set of rules, it can be well worth it.