Mishneh Torah (Rambam) משנה תורה

One who recites the first verse of Kri'at Shema - i.e., Shema Yisrael... - without intention, does not fulfill his obligation. [One who recites] the rest without intention fulfills his obligation. Even a person studying Torah in his usual way or proofreading these portions at the time of Kri'at Shema fulfills his obligation provided he concentrates his intention for the first verse.

A person may recite [the Shema] as he is, whether standing, walking, lying down or riding on the back of an animal. It is forbidden to recite the Shema while lying face down on the ground or flat on one's back with his face pointing upwards. However, one may recite it lying on his side. A particularly obese person who cannot turn over onto his side or a sick person should lean slightly to the side and [then] recite it.

A person who is walking on foot must stop for the first verse. He may recite the rest while walking. If one is sleeping, we should disturb him by awakening him until he reads the first verse. From that point on, if he is overcome by sleep, we are not obligated to disturb him.

A person who is involved in work must stop while he recites the whole first section. Artisans must also interrupt their work for the first section, in order that their recitation should not be haphazard. They may recite the rest while working in their normal manner. Even one standing in a tree or on top of a wall may read [the Shema] where he is, reciting the blessings before and after it.

A person who is studying Torah when the time to recite the Shema arrives should stop to recite the Shema with the blessings before and after it. One who is involved in community matters should not stop, but rather finishes his work and reads the Shema if there is still time left.

A person who is eating, is in the bathhouse, is having a haircut, is working with skins or is involved in court, should complete [his task] and recite the Shema afterwards. If he fears that the time for its recitation will pass, and, [therefore,] stops to recite it, he has acted in a praiseworthy fashion.

A person who immerses in a ritual bath and is able to come up and dress before sunrise, should do so, and [then] recite [the Shema]. If he is afraid that perhaps the sun will rise before he can recite the Shema, he should cover himself with the water in which he stands and recite the Shema. He should not cover himself with putrid water that has an unpleasant odor or with water that has been used for soaking flax or with water so clean that his nakedness is visible. However, he may cover himself with murky water that has no unpleasant odor and recite [the Shema] where he is.

While reciting the Shema, one should not gesture with his eyes or lips, or point with his fingers, in order that his reading not be haphazard. If one were to do this, although he does fulfill his obligation, he has acted improperly. One should recite the Shema so that his words are audible to himself. [However, even] if he does not do this, he fulfills his obligation. One must enunciate the letters clearly. [However, even] if he does not do this, he fulfills his obligation.

How must one enunciate? He must be careful not to pronounce [a letter with] a strong dagesh as if there were no dagesh, or [a letter with] no dagesh as if there were one. Nor should one pronounce the silent sheva or silence the pronounced sheva. Therefore, one must pause between two words in which the first word ends with the same letter with which the second word begins. For example, when reading בכל לבבך (bechol levavcha) (Deuteronomy 6:5), one should pause slightly between בכל (bechol) and לבבך (levavcha). [One should act] similarly in the cases of ואבדתם מהרה (va'avad'tem meheirah) (Deuteronomy 11:17) and הכנף פתיל (hacanaf p'til) (Numbers 15:38). One must also pronounce distinctly the zayin of תזכרו (tizkeru) (Numbers 15:40). One should sufficiently elongate the dalet in אחד (echad) (Deuteronomy 6:4) in order to proclaim God's sovereignty over the Heaven and the Earth, and all four directions. The chet in אחד (echad, ibid.) should not be shortened so that the word sounds like איחד (ee-chad).

A person may recite the Shema in any language he understands. One who recites in a foreign language must be as scrupulous in his enunciation as if he were reciting it in the Holy Tongue.

One who reads [the Shema] out of order does not fulfill his obligation. This refers to the order of the verses. However, were one to reverse the order of the sections, even though it is not permitted, I hold that he does fulfill his obligation, since these sections are not sequential in the Torah. To recite a verse and then repeat it again is improper. One who reads a word and then repeats it, such as one who recites Shema, Shema, should be silenced.

If one reads intermittently, he fulfills his obligation, even if he pauses between each reading an amount of time sufficient to complete the entire Kri'at Shema. This refers to the one who recites it in order. If one recites it while drowsy - i.e., not fully awake, but not fast asleep - he fulfills his obligation, as long as he was fully awake while reciting the first verse.

One who is unsure whether or not he recited the Shema, should recite it with the blessings before and after it. However, if he is sure that he recited the Shema, but is in doubt regarding whether he recited the blessings before and after it, he need not recite the blessings again. A person who made a mistake while reciting [the Shema] should return to the point of his mistake. If one becomes confused and forgets which section he has just completed, he should return to the first section - i.e., "And you shall love God, your Lord" (Deuteronomy 6:5).

A person who errs in the middle of a section and is unaware of where he paused, should return to the beginning of that section. One who recited וכתבתם (uch'tavtam) but does not know whether or not he recited uch'tavtam of [the section of] "Shema" or of [the section of] והיה אם שמוע (And if you will listen), should return to uch'tavtam of "Shema." However, if his doubt arises only after having recited למען ירבו ימיכם (In order that your days be multiplied) (Deuteronomy 11:21), he need not return, because [we assume] he has recited in accordance with the natural pattern of his speech.

[The following rules apply when] one encounters other people or is approached by them while reciting the Shema. If he is between sections, he should stop and greet those he is obligated to honor - e.g., his father, his teacher or anyone greater than he in learning. He may return the greetings of any person who initiates the friendly exchange.

If one is in the middle [of a section], he may stop and initiate an exchange of greetings only with someone of whom he is afraid - e.g., a king or tyrant. However, he may return the greetings of those he is obligated to honor - e.g., his father or his teacher.

These are the intervals between the sections: between the first blessing and the second; between the second [blessing] and Shema; between the first and second sections of Kri'at Shema; between the second and third sections of Kri'at Shema. Between these sections, one initiates an exchange with one whom it is his duty to honor and responds to the greetings of anyone. However, the interval between the end of the third section of Kri'at Shema and [the paragraph beginning with] Emet v'yatziv is considered the middle of a section, and one may interrupt only to greet one of whom one is afraid, or to respond to the greetings of someone one is obligated to honor.