https://www.bloomberg.com/news/articles/2017-12-21/tax-free-bitcoin-to-ether-trading-in-u-s-to-end-under-gop-planThe new tax law explicitly makes exchanges between cryptocurrencies taxable as of January 1.
This means that when you (for example) buy Monero with Bitcoin, you have to treat the trade as if you sold Bitcoin for cash and bought the Monero with cash, and must declare the gain/loss on the Bitcoin you sold as a taxable event.
Until now there has been controversy as to whether or not cryptocurrency exchanges could be treated as "like kind" exchanges. In a like kind exchange the tax basis for the currency sold is carried forward into the currency bought, and no tax is due until the second currency is later sold. This option has now been ended.
This might be good news for those of us who have not been claiming like kind status on our crypto trades as it kind of implies that we could get away with doing so for the 2017 tax year.
