This article needs additional citations for verification. (May 2011) (Learn how and when to remove this template message)
Slitherlink is played on a rectangular lattice of dots. Some of the squares formed by the dots have numbers inside them. The objective is to connect horizontally and vertically adjacent dots so that the lines form a simple loop with no loose ends. In addition, the number inside a square represents how many of its four sides are segments in the loop.
Other types of planar graphs can be used in lieu of the standard grid, with varying numbers of edges per vertex or vertices per polygon. These patterns include snowflake, Penrose, Laves and Altair tilings. These add complexity by varying the number of possible paths from an intersection, and/or the number of sides to each polygon; but similar rules apply to their solution.
Slitherlink is an original puzzle of Nikoli; it first appeared in Puzzle Communication Nikoli #26 (June 1989). The editor combined two original puzzles contributed there. At first, every square contained a number and the edges did not have to form a loop.
Slitherlink video games have been featured for the Nintendo DS handheld game console, with Hudson Soft releasing Puzzle Series Vol. 5: Slitherlink in Japan on November 16, 2006, and Agetec including Slitherlink in its Nikoli puzzle compilation, Brain Buster Puzzle Pak, released in North America on June 17, 2007.
- Nikoli's English page on Slitherlink
- On the NP-completeness of the Slitherlink Puzzle - Slitherlink is NP-complete
- Site discussing non-grid forms of Slitherlink including snowflake, penrose, laves, and altair
- KwontomLoop - A free site with daily slitherlink puzzles varying in difficulty. Also includes a ranking system with other players.
- Conceptis puzzles: Slitherlink techniques - This site shows some advanced solving techniques.
- games.softpedia.com - Slitherlink downloadable game. This generates puzzle at various levels and dimensions. Also you can upload a puzzle (external to the site) to solve it.
- krazydad.com - Download a large number of printable PDF books of slitherlink puzzles of various levels.
-  - A suggested notational system to document slitherlink puzzles.
- Loopy - One of the many simple desktop puzzle games for Windows/Unix by Simon Tatham.