There are two types of sonnet: the Italian or Petrachan sonnet and the Elizabethan or Shakespearean sonnet.  The Elizabethan or Shakespearean sonnet relates to the time period following the Renaissance (the divine and the universal) and not strictly to Shakespeare - himself - and to Elizabeth I in England. Shakespeare is credited with having perfected the technique:

but he is certainly not the only poet to use this sonnet form.

The Elizabethan sonnet became extremely popular

 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.

 The influence of the Petrachan sonnet cannot go unsaid and once the sonnet form had been introduced to England, it became a very popular form of poetry. There was an anti-Petrarchan convention at about the time Shakespeare was writing his sonnets,

which satirized or exploited traditional motifs and styles.

Shakespeare's sonnets at the time were compared to 

his predecessors and contemporaries, including Sidney, Sir Thomas Wyatt, Henry Howard, Earl of Surrey, Samuel Daniel, and Edmund Spenser.

 The Elizabethan sonnet is

made up of four quatrains ... and ends with a rhyming couplet. The rhyme scheme is abab cdcd efef gg.

Each sonnet inevitably tells a love story or links to the beauty of a woman.  The 'problem' that is encountered is introduced in the first two quatrains whereafter there is a change in the tone. The rhyming couplet generally summarizes the poem.  

Elizabethan sonnets also include metaphors, paradox, allusions to classical mythology, alliteration, word repetition, pastoral imagery, and an overall theme. A repeating line, metaphor, or idea brings it together.

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