Is it illegal to provide links of other sites in your own websites or blog?

Answer 1

No, it is not illegal unless specified (for example, linking to an insider's page on a government site may be illegal if the address is considered confidential). In most cases it is not illegal, and may in fact be encouraged.

It really depends on the administrator of the website you want to link to - he may, for example, restrict you to linking to certain pages instead of just to resources within them (hot-linking), but probably won't disallow you to link in general.

In most cases, linking to other websites concerning similar material, further reading, or citing your sources is encouraged as a good practice - no web server is an island, so to speak. Also, citing your sources and giving credit where credit is due is always a good thing to do, and others will think better of those that do it. In the end, the article/post/information will have to stand on its own merit, and hiding your sources (except in cases where it may be prudent) is generally considered an act of fear, a weakness, a discredit to the author.

The internet is a "network of networks", but it's also a network of information-bearing services. If you believe that reading what you're trying to link to would be beneficial to the reader in some way, and the author has not disallowed linking to their posting, go ahead and link away.

Curious note: linking to what some people would call "questionable material" like .torrent files, or even hosting them, is legal as well, no matter what the media lobbyists will say about it - these files are just descriptors for other files (say, a map and a city plan, in a manner of speaking), and contain no copyright-infringing material on their own.