My sister is getting married later this year.  My boyfriend and I
would like to get engaged prior to her wedding, but my sister has
declared that it is inappropriate & will only steal her limelight. 
Is there any formal etiquette as it concerns this issue?

I could find no etiquette book that specifically addressed your
question; however, as the author of a wedding book, I hope you will
accept my thoughts on this without the back up of other people's
opinions.

Frankly, there is no etiquette about holding off an announcement or an
engagement, because nothing should stop a couple from pursuing
marriage if that's what they desire. There's no reason you can't
become engaged and announce your engagement whenever you like.

Under the circumstances, you may want to consider a few things, however:

When do you wish to get married? If the wedding will be some time
away, you might consider being "secretly" engaged, then announce your
engagement *after* your sister's wedding. I, myself, had a secret
engagement, and it was a lot of fun. Of course, the secret only lasted
a week or so :)

Also think about the personality of your sister. Does she frequently
complain? Does she often feel competitive? Does she usually put "her
stuff" before your feelings? Some people, unfortunately, are
impossible to please...so there's no use trying to please them.

You might approach your sister, reminding her how eager she was to be
engaged, and explain that you're eager and excited, too. Let her know
that it's just a coincidence you're getting engaged around the same
time she is. Isn't she excited for you? Tell her that it could be a
lot of fun; that you *could,* if she desires, do things like
engagement parties, bridal showers, etc. together. BUT if she'd
rather, it won't hurt your feelings to have separate parties, etc. Let
her know that you don't want to steal any of her thunder, but make it
clear that you have a right to become engaged and get married just as
much as she does.

Then go out of your way to make sure you don't step on her toes. It
might be helpful to find out, for example, when she's mailing
engagement notices, invitations, etc., so that you can time yours at
least some weeks *after* hers. If your parents are involved in the
wedding planning, make sure that the help they give you doesn't
interfere with the help your sister longs for. But also use good
sense. Just because your sister feels sensitive about this issue,
doesn't mean that you shouldn't fully enjoy your engagement and all
that goes with it.

Best wishes,
Kriswrite

While I was hoping that there might be a "rulebook" out there to
address my issue (there does not seem to be one), the researcher that
answered my question posed some great things to think about. (and I
was happy to see that she has written a book on a related subject!). 
Many thanks.

Here's something that may be of interest. It's hard to find a better
authority than Miss Manners:

Dear Miss Manners,
I feel guilty even writing this letter, but I know you'll advise me
well and put this issue to rest. Here is my predicament: My younger
sister has recently announced her engagement, and I feel very slighted
by it because she didn't bother to ask me if I would have a problem
with her getting married before I do.

I have been dating my boyfriend for nearly five years, and we were
very close to becoming engaged ourselves when this was announced. Of
course, I am very happy for my younger sister, but I thought that it
was proper and encouraged to discuss this with your older sister when
the time came, especially given the circumstances. I know this is how
my mother and her sisters went about doing things, and don't see why
it would be abandoned in this day and age. Maybe I'm a whiner, but I
feel a lot like my spotlight was stolen! Please advise.

Gentle Reader,
In this day and age? Even in the distant past, Miss Manners recalls
that only the Leahs liked this system, not the Rachels. Her advice is
therefore intended for your sister: Get married now. When your elder
sister's suitor discovers that she begrudges happiness to her own
relatives because she feels it takes the spotlight away from her, he
will get off the verge. Then you will have to wait another five years
before she brings someone else to that verge.

http://women.msn.com/a454553.armx

I was involved in the same situation.  I proposed to my wife a few
monthes before my sister's wedding.  Of course I told my sister what I
was going to do and she briefly objected but came to her senses and
realized that one should not put off one's happiness for another.  She
felt no ill will and even helped in the planning process.  If your
sister truly cares she will not see your hapiness as "stealing your
limelight" but rather be happy for you.

Bowler-ga

Regarding the "limelight"...

In a few months my husband and I will celebrate our 24th wedding
anniversary. We got married in the living room of our first house.
There were twelve guests. My mom baked the wedding cake. My brother
and sister took the photographs. We drank a wedding toast from a $4.00
bottle of champagne.

I'd like to remind folks that the really important thing is not the
wedding, but the marriage.

Thanks very much for this.  I was hoping that Miss Manners would come
through somehow!! :)

By the way, I am in total agreement as it concerns the marriage vs the
wedding.  While my sister is planning "the wedding of the century"
(read: 150+ guests), my boyfriend and I are planning a civil ceremony
with only the closest of friends and relatives (read:  less than 50). 
Again, many thanks.