The trefoil is perhaps the easiest knot to find in "nature", and is topologically equivalent to the interlaced form of the common Christian and pagan "triquetra" symbol [12]:
Logo of Caixa Geral de Depositos, Lisboa [1]

A knot consists of two harts in Kolam [2]

A basic form of the interlaced Triquetra; as a Christian symbol, it refers to the Trinity


Further images...
Trefoil/triquetra without outside corners (made from straight lines and 240° circular arcs)

Triquetra made from circular arc ribbons




A trefoil near the Hollander York Gallery [4]

Trefoil of three intersecting circles

Trefoil depicted in nonthreefold form

3D depiction in nonthreefold form

A hagfish tying itself in a knot to escape capture. [5]

One version of the Germanic "Valknut" symbol



In the form of an architectural trefoil


Alternate Valknut depiction

Simple overhand knot of practical knottying

Tightly folded pentagonal overhand knot

Visually fancier square trefoil

Trefoil knot as impossible object

Logo of the Caixa Geral de Depósitos with white background

The NeverEnding Story logo is a connected sum of two trefoils. [7]

Mike Hutchings' Rope Trick [8]

Thurston's Trefoil  Figure Eight Trick [9]



Nonprime (compound) versions
Two trefoils (singleclosedloop version of the "granny knot" of practical knottying).
Two trefoils (singleclosedloop version of the "square knot" of practical knottying)
Three trefoils (symmetrical).
Four trefoils (Celtic or pseudoCeltic decorative knot which fits in square)
Three trefoils along a closed loop which itself is knotted as a trefoil.
For configurations of two trefoils along a closed loop which are prime, see 8_15 and 10_120. For a configuration of three trefoils along a closed loop which is prime, see K13a248. For a prime link consisting of two joined trefoils, see L10a108.