The Major League Baseball draft (officially the Rule 4 Draft; also known as the first-year player draft or amateur draft) is the primary mechanism by which Major League Baseball (MLB) assigns amateur baseball players from high schools, colleges, and other amateur baseball clubs to its teams. The draft order is determined by a lottery system, starting in 2023, where teams that did not make the postseason in the previous year participate in a lottery process to determine the first six picks. The team with the worst record has the best odds of receiving the first pick. Prior to 2023, the draft order was based on the previous season's standings, with the worst team selecting first.

The first amateur draft was held in 1965. Unlike most sports drafts, the MLB draft is held mid-season, taking place in July since 2021. Another distinguishing feature of the draft compared to those of other North American major professional sports leagues is its sheer size: currently, the draft lasts for 20 rounds (600+ selections), in addition to compensatory picks introduced in 2021; until 2019, it lasted up to 40 rounds (1,200+ selections), and until 2011, it lasted up to 50 rounds (1,500+ selections). In contrast, the NFL draft lasts seven rounds (260 selections), the NHL entry draft lasts seven rounds (224 selections), the MLS SuperDraft lasts three rounds (87 selections), the CFL draft lasts eight rounds (72 selections), and the NBA draft is only two rounds (60 selections).

On March 26, 2020, MLB and the Major League Baseball Players Association (MLBPA) reached a deal that included the option to shorten that year's draft to five rounds, and halve the 2021 draft to 20 rounds. On March 10, 2022, after agreeing on a new collective bargaining agreement, it was decided that the first-round order would be based on a lottery participated by 18 non-postseason teams to determine the first six picks, starting with the 2023 draft. The remaining first-round picks and subsequent rounds are determined by the previous season's win-loss records for the first 18 selections in each round, followed by playoff finishes.

Before the draft Major League Baseball has used a draft to assign minor league players to teams since 1921.Before the advent of the farm system, minor league players were under contract to their respective teams, rather than to a parent club. The minor league draft (known today as the Rule 5 draft) was later used to redistribute minor league players already under contract to major league teams. In 1936, the National Football League held the first amateur draft in professional sports.Staudohar, Lowenthal, and Lima, pp. 27–28. A decade later, the National Basketball Association instituted a similar method of player distribution. However, the player draft was controversial. Congressman Emanuel Celler questioned the legality of drafts during a series of hearings on the business practice of professional sports leagues in the 1950s.Hearings before the Antitrust Subcommittee, Committee on the Judiciary,, 85th Cong., 1st Sess. (1957) (testimonies of Chuck Bednarik, Red Grange, Kyle Rote, and Jackie Robinson). Successful clubs saw the draft as anti-competitive. Yankees executive Johnny Johnson equated it with communism. At the same time, Pulitzer Prize-winning sports columnist Arthur Daley compared the system to a "slave market."

Prior to the implementation of the first-year player draft, amateurs were free to sign with any Major League team that offered them a contract. As a result, wealthier teams such as the New York Yankees and St. Louis Cardinals were able to stockpile young talent, while poorer clubs were left to sign less desirable prospects.

In 1947, Major League Baseball implemented the bonus rule, a restriction aimed at reducing player salaries, as well as keeping wealthier teams from monopolizing the player market. In its most restrictive form, it forbade any team which gave an amateur a signing bonus of more than $4,000 from assigning that player to a minor league affiliate for two seasons. If the player was removed from the major league roster, he became a free agent. The controversial rule was repealed twice, only to be re-instituted.

The bonus rule was largely ineffective. There were accusations that teams were signing players to smaller bonuses, only to supplement them with under-the-table payments. In one famous incident, the Kansas City Athletics signed Clete Boyer, kept him on their roster for two years, then traded him to the Yankees just as he became eligible to be sent to the minor leagues. Other clubs accused the Yankees of using the Athletics as a de facto farm team, and the A's later admitted to signing Boyer on their behalf. By 1964, the total amount of money paid in signing bonuses to amateur players was greater than the amount spent on major league salaries; it was the bidding war that year for Rick Reichardt, who signed with the California Angels for the then outrageous bonus of $200,000, (about $1.8 million today) that finally led to the implementation of the draft.

Major League clubs voted on the draft during the 1964 Winter Meetings. Four teams—the New York Yankees, St. Louis Cardinals, Los Angeles Dodgers, and New York Mets—attempted to defeat the proposal, but they failed to convince a majority of teams, and in the end only the Cardinals voted against it.

The draft MLB player transactions are governed by The Official Professional Baseball Rules Book, within which, Rule 4 governs the "First-Year Player Draft". Due to its place in the rules book, MLB's amateur draft is sometimes referred to as the "Rule 4 draft"; there is also a distinct Rule 5 draft.

Major League Baseball's first amateur draft was held on June 8–9, 1965, in New York City. Teams chose players in reverse order of the previous season's standings, with picks alternating between the National and American Leagues. With the first pick, the Kansas City Athletics took Rick Monday, an outfielder from Arizona State University.

Originally, three separate drafts were held each year. The June draft, which was by far the largest, involved new high school graduates, as well as college seniors who had just finished their seasons. Another draft was held in January, which typically involved high school players who graduated in the winter, junior college players, and players who had dropped out of four-year colleges. Junior college players were required to wait until their current season was completed before they could sign. Finally, there was a draft in August for players who participated in amateur summer leagues. The August draft was eliminated after only two years, while the January draft lasted until 1986.

Influence of the draftee's age Early on, the majority of players drafted came directly from high school. Between 1967 and 1971, only seven college players were chosen in the first round of the June draft. However, the college players who were drafted outperformed their high school counterparts by what statistician Bill James called "a laughably huge margin."Staudohar, Lima, and Lowenthal, p. 39. By 1978, a majority of draftees had played college baseball, and by 2002, the number rose above sixty percent. While the number of high school players drafted has dropped, those picked have been more successful than their predecessors. In a study of drafts from 1984 to 1999, Baseball Prospectus writer Rany Jazayerli concluded that, by the 1990s, the gap in production between the two groups had nearly disappeared. In October 2011, Jazayerli presented another research study which included an analysis of those players drafted since 1965, but instead of breaking them into college or high school draftees, he segregated them by their age on draft day. In the study published in Baseball Prospectus, which included a follow-up article of the financial benefits, Jazayerli concluded that the very young players return more value than expected by their draft slots. In Jazayerli's study he looked at the statistics and broke draftees into five distinctive groups based on their age and being drafted in the early rounds. Jazayerli's defined a "very young" player as those who are younger than 17 years and 296 days on draft day. Since the inception of the draft, the youngest player ever drafted in an early round is Alfredo Escalera. Escalera was drafted by the Kansas City Royals in the eighth round of the 2012 draft at 17 years and 114 days. Jazayerli's study does not clearly demonstrate the influence of the player's age when drafted in a late round.

Economic impact Initially, the draft succeeded in reducing the value of signing bonuses. In 1964, a year before the first draft, University of Wisconsin outfielder Rick Reichardt was given a record bonus of $200,000 () by the California Angels. Without competition from other clubs, the Athletics were able to sign Rick Monday for a bonus of only $104,000 (). It would take until 1979 when USC pitcher Bill Bordley received a bonus higher than Reichardt's.There is some disagreement over who was the first player to surpass Reichardt's bonus. Staudohar claims that Darryl Strawberry's 1980 bonus equaled Reichardt's, but it was actually worth only $200,000 ($ today). Jazayerli credits Andy Benes, who signed with the San Diego Padres for $235,000 ($ today) in 1988. Baseball America lists Todd Demeter, a career minor-leaguer drafted by the New York Yankees, as surpassing the milestone when he signed for a $208,000 ($ today) bonus in 1979.

Player salaries continued to escalate through the 1980s. In 1986, Bo Jackson became the first draftee to sign a total contract (signing bonus and salary) worth over $1 million ($ today). Jackson, a Heisman Trophy-winning football player for Auburn University, was also the first overall choice in the National Football League draft, and was offered a $7 million ($ today) contract to play football for the Tampa Bay Buccaneers.

High school players possessed additional leverage, as they had the option of attending college and re-entering the draft the next year. Agent Scott Boras routinely exploited this advantage to increase the contracts of his clients. In 1990, Boras client Todd Van Poppel signed a $1.2 million ($ today) contract with Oakland Athletics, after committing to play for the University of Texas. The following year, Boras negotiated a $1.55 million ($ today) contract for Yankees first round pick Brien Taylor, who had said he would attend junior college if he did not receive a contract equal to Van Poppel's. By June 2009, a figure as high as $15 million was floated for collegiate pitcher Stephen Strasburg.

Increasingly, teams drafted based on whether or not a player was likely to sign for a particular amount of money, rather than on his talent. This became known as a "signability pick". Before the 1992 draft, team owners unilaterally decided to extend the period of time a team retained negotiating rights to a player from one year to five. In effect, the rule prohibited a high school draftee from attending college and re-entering the draft after his junior or senior seasons. The Major League Baseball Players Association filed a legal challenge, but Major League Baseball argued that, since the Players Association did not represent amateur players, it was not necessary for the union to agree to the change. An arbitrator ultimately decided that any change to draft articles must be negotiated with the Players Association.Staudohar, Lowenthal, and Lima, pp. 32–33.

Media exposure

The first-year player draft has historically had far less media exposure than its counterparts in the other leagues for three primary reasons: