We do not know when Shakespeare composed his sonnets, though it is possible that he wrote them over a period of several years, beginning, perhaps, in 1592 or 1593. Some of them were being circulated in manuscript form among his friends as early as 1598, and in 1599 two of them—138 and 144—were published in The Passionate Pilgrim, a collection of verses by several authors. The sonnets as we know them were certainly completed no later than 1609, the year they were published by Thomas Thorpe under the title Shake-speares Sonnets. Most scholars believe that Thorpe acquired the manuscript on which he based his edition from someone other than the author. Few believe that Shakespeare supervised the publication of this manuscript, for the text is riddled with errors. Nevertheless, Thorpe's 1609 edition is the basis for all modern texts of the sonnets.

With only a few exceptions—Sonnets 99, 126, and 145—Shakespeare's verses follow the established English form of the sonnet. Each is a fourteen-line poem in iambic pentameter, comprising four sections: three quatrains, or groups of four lines, followed by a couplet of two lines. Traditionally, a different—though related—idea is expressed in each quatrain, and the argument or theme of the poem is summarized or generalized in the concluding couplet. It should be noted that many of Shakespeare's couplets do not have this conventional effect. Shakespeare did, however, employ the traditional English sonnet rhyme-scheme: abab, cdcd, efef, gg.

Shakespeare's 154 sonnets, taken together, are frequently described as a sequence, and this is generally divided into two sections. Sonnets 1-126 focus on a young man and the speaker's friendship with him, and Sonnets 127-52 focus on the speaker's relationship with a woman. However, in only a few of the poems in the first group is it clear that the person being addressed is a male. And most of the poems in the sequence as a whole are not direct addresses to another person. The two concluding sonnets, 153 and 154, are free translations or adaptations of classical verses about Cupid; some critics believe they serve a specific purpose—though they disagree about what this may be—but many others view them as perfunctory.

The English sonnet sequence reached the height of its popularity in the 1590s, when the posthumous publication of Sir Philip Sidney's Astrophel and Stella (1591) was widely celebrated and led other English poets to create their own sonnet collections. All of these, including Shakespeare's, are indebted to some degree to the literary conventions established by the Canzoniere, a sonnet sequence composed by the fourteenth-century Italian poet Petrarch. By the time Shakespeare wrote his sonnets, there was also an anti-Petrarchan convention, which satirized or exploited traditional motifs and styles. Commentators on Shakespeare's sonnets frequently compare them to those of his predecessors and contemporaries, including Sidney, Sir Thomas Wyatt, Henry Howard, Earl of Surrey, Samuel Daniel, and Edmund Spenser.

The principal topics of twentieth-century critical commentary on the sonnets, however, are their themes and poetic style. Analyses of formal elements in the poems include examinations of the rhetorical devices, syntax, and diction Shakespeare employed here. The multiple and indefinite associations of his words and phrases have proved especially intriguing—and problematic—for scholars as well as general readers. The complexity and ambiguity of Shakespeare's figurative language is also a central critical issue, as is the remarkable diversity of tone and mood in the sequence. Shakespeare's departures from or modifications of the poetic styles employed by other sonneteers have also drawn a measure of critical attention.

Many of Shakespeare's themes are conventional sonnet topics, such as love and beauty, and the related motifs of time and mutability. But Shakespeare treats these themes in his own, distinctive fashion—most notably by addressing the poems of love and praise not to a fair maiden but instead to a young man; and by including a second subject of passion: a woman of questionable attractiveness and virtue. Critics have frequently called attention to Shakespeare's complex and paradoxical representation of love in the sonnets. They have also discussed at length the poet-speaker's claim that he will immortalize the young man's beauty in his verses, thereby defying the destructiveness of time. The themes of friendship and betrayal of friendship are also important critical issues, as is the nature of the relationship between the speaker and the youth. The ambiguous eroticism of the sonnets has elicited varying responses, with some commentators asserting that the relationship between the two men is asexual and others contending that it is sexual.

Because these lyrics are passionate, intense, and emotionally vivid, over the centuries many readers and commentators have been convinced that they must have an autobiographical basis. There is, however, no evidence that this is so. Nevertheless, there has been endless speculation about what these sonnets may tell us about their creator, and researchers have attempted to identify the persons who were the original or historical models for the persons the speaker refers to and addresses. The fact remains, however, that we do not know to what degree Shakespeare's personal experiences are reflected in his sonnets; nor do we know with any measure of certainty whether the persons depicted in these poems are based on specific individuals or are solely the product of Shakespeare's observation, imagination, and understanding of the human heart.

Contradictions and uncertainties are implicit in Shakespeare's sonnets. Both individually and as a collection, these poems resist generalities and summations. Their complex language and multiple perspectives have given rise to a number of different interpretations, all of which may at times seem valid—even when they contradict each other. Few critics today read the sonnets as personal allegory. Indeed, most commentators assert that speculation about what these verses may imply about Shakespeare's life, morals, and sexuality is a useless exercise. The speaker is as closely identified with each reader as he is with the writer who created him. His confused and ambiguous expressions of thought and emotion heighten our own ambivalent feelings about matters that concern us all: love, friendship, jealousy, hope, and despair.