Historical kana orthography

The , or , refers to the in general use until orthographic reforms after World War II; the current orthography was adopted by Cabinet order in 1946. By that point the historical orthography was no longer in accord with Japanese pronunciation. It differs from modern usage ("Gendai kana-zukai") in the number of characters and the way those characters are used. There was considerable opposition to the official adoption of the current orthography, on the grounds that the historical orthography conveys meanings better, and some writers continued to use it for many years after.
The historical orthography is found in almost all Japanese dictionaries, such as "Kōjien." In the current edition of the "Kōjien," if the historical orthography is different from the modern spelling, the old spelling is printed in tiny katakana between the modern kana and kanji transcriptions of the word. Ellipses are used to save space when the historical and modern spellings are identical. Older editions of the "Kōjien" gave priority to the historical orthography.
The historical orthography should not be confused with "hentaigana," alternate kana that were declared obsolete with the orthographic reforms of 1900.
General differences.
In historical kana usage:
Most of the historical kana usage has been found to accurately represent certain aspects of the way words sounded during the Heian period. As the spoken language has continued to develop, some orthography looks odd to the modern eye. As these peculiarities follow fairly regular patterns, they are not difficult to learn. However, some of the historical kana usages are simply mistakes. For example, 
Those familiar with Japanese writing may notice that most of the differences apply to words which are usually written in Kanji anyway, and so would require no changes to switch from one Kana system to another (unless furigana are employed). In particular, yōon sounds occur almost exclusively in the Chinese-derived readings that are usually only seen in Kanji compounds (although not entirely; "kyō" "today," written "kefu" in the old system, is a native Japanese word), and therefore do not look any different (without furigana). The relative lack of difference in appearance in practice between the two systems was a major reason the spelling reform succeeded, and also why the three grammatical particles "o", "e", "wa" continue to be written as "wo", "he", and "ha" instead of "o", "e", and "wa"; many felt that changing these exceedingly common spellings would unnecessarily confuse readers. It is also for this reason that many character dictionaries continue to include the historical spellings, since they are relevant there.
Some forms of unusual kana usage are not, in fact, historical kana usage. For example, writing "dojō" (loach, a sardine-like fish) in the form "dozeu" is not historical kana usage (which was "dodiyau"), but a kind of slang writing originating in the Edo period. 
Examples.
Here are some representative examples showing the historical and modern spellings and the kanji representation.
The table at the bottom gives a more complete list of the changes in spelling patterns.
Current usage.
Historical kana usage can be used to look up words in larger dictionaries and dictionaries specializing in old vocabulary, which are in print in Japan. Because of the great discrepancy between the pronunciation and spelling and the widespread adoption of modern kana usage, historical kana usage is almost never seen, except in a few special cases. Companies, shrines and people occasionally use historical kana conventions such as (Ebisu), notably in Yebisu beer, which is written "webisu" but pronounced ebisu. Also, some long-standing company names retain yōon in full-sized kana, like (Canon) and (Fujifilm).
In addition, alternate kana letterforms, known as hentaigana , have nearly disappeared. A few uses remain, such as "kisoba", often written using obsolete kana on the signs of soba shops.
The use of "wo", "he", and "ha" instead of "o", "e", and "wa" for the grammatical particles "o", "e", "wa" is a remnant of historical kana usage.
Table of differences.
The following tables summarize every possible historical spelling for the syllables which were spelled differently under the historical system. When more than one historical spelling is given for a particular modern spelling, the various historical spellings were etymologically (and at one point phonetically) distinct and occurred in different words (i.e., are not merely different ways to spell the same word). The tables are sorted using the gojūon ordering system.
Note that the dakuten (voicing mark) was frequently omitted as well, as in the station sign at right. 
Romanization.
Readers of English occasionally encounter words romanized according to historical kana usage. Here are some examples, with modern romanizations in parentheses: