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Convert date to specific format if I don't know source date format

I want to convert date to a specific format (e.g. en-US MM/dd/yyyy) and I am aware about normal method to parse it.
But in my case I'm unaware about the source date format. Source date format is subject to change as per server environment. It can be en-US or en-GB.
e.g. DateTime dt = DateTime.Now;
'dt' can be '27/03/2014' or '03/27/2014'.
How to convert the source date to en-US format if I don't know source date format?
(string format would be fine - MM/dd/yyyy e.g. "03/27/2014").

If you don't know the source format, there is a chance of getting errors while trying to convert. For example, try converting:
05/01/2013
A computer wouldn't be able to identify the date in such a case. It could result in two outputs: 05 Jan, 2013 or 01 May, 2013.

DateTime.Now.toString("yyyy-MM-dd"); //toString(specify format)
try this one

DateTime result;
if (!DateTime.TryParseExact(inputString, "dd/MM/yyyy", out result)
result = DateTime.ParseExact(inputString, "MM/dd/yyyy");
OR
DateTime result;
if (!DateTime.TryParse(inputString, out result)
result = DateTime.ParseExact(inputString, CultureInfo.InvariantCulture, DateTimeStyles.None);

If you know your environment will always be the deciding factor, why not just use that?
Try some variation of the following:
string yourFormat = ... // Whatever is your default format
if(Thread.CurrentThread.CurrentCulture.Name == "en-US")
{
yourFormat = "MM/dd/yyyy";
}
else (if Thread.CurrentThread.CurrentCulture.Name == "en-GB")
{
yourFormat = "dd/MM/yyyy";
}
DateTime d = DateTime.ParseExact(inputString, yourFormat, null)

How to convert the source date to en-US format if I don't know source date format?
You need to know the source date format, only then can you convert it to the required date format.
As wiero has rightly said in the comments "If you have 01/02/2014 depending its 1 February or 2 January. You have to know how to read it".
The default format of the object returned by DateTime.Now will be the one specified in your server setting, check the screenshot below:

Referring to #DarkWanderer's comment in question:
DateTime object has nothing to do with format.
Just needed to convert it to the specific format using ToString("MM/dd/yyyy").
I was using Parse() method to convert but it will not work. BToString() method is surely a way.
This will work: dt.Tostring("MM/dd/yyyy");
Thanks #DarkWanderer.

Convert string to date time and format to specific format in string

the string is 20131024174621 which is year =2013, month=10, date=24, hours=17, minutes=46, seconds=21
What I am trying to do is to convert and format it into 2013-10-24 17:46:21.
I have tried my luck as the code below however it return such error :
String was not recognized as a valid DateTime.
String timestamp = "20131024174621";
String converted = DateTime.Parse(timestamp).ToString("yyyy-MM-dd HH:mm:ss");
What should be the way of doing it right?

You have to use ParseExact.
void Main()
{
String timestamp = "20131024174621";
var date = DateTime.ParseExact(timestamp, "yyyyMMddHHmmss", CultureInfo.InvariantCulture);
Console.WriteLine (date.ToString("yyyy-MM-dd HH:mm:ss"));
}
Output:
2013-10-24 17:46:21

DateTime.ParseExact( timestamp, "yyyyMMddHHmmss", CultureInfo.InvariantCulture ).ToString( "yyyy-MM-dd HH:mm:ss" );

Since other two answer is correct, I want to point the root of your problem.
DateTime.Parse method uses Standard Date and Time Format Strings. From How Standard Format Strings Work
In a formatting operation, a standard format string is simply an alias
for a custom format string. The advantage of using an alias to refer
to a custom format string is that, although the alias remains
invariant, the custom format string itself can vary. This is important
because the string representations of date and time values typically
vary by culture. For example, the "d" standard format string indicates
that a date and time value is to be displayed using a short date
pattern. For the invariant culture, this pattern is "MM/dd/yyyy". For
the fr-FR culture, it is "dd/MM/yyyy". For the ja-JP culture, it is
"yyyy/MM/dd"
In 20131024174621 string, you need yyyyMMddHHmmss format for your current culture. Looks like your culture doesn't have this format and that's why you get this error.
For this kind of non-standart format string, you can use custom date format.
Any string that is not a standard date and time format string is
interpreted as a custom date and time format string.
As I wrote in third paragraph, this kind of date formats is based on culture. When you have this kind of custom date strings, in most case using DateTime.ParseExact Method (String, String, IFormatProvider) with specific culture is the best choice.

Output DateTime date but no time using only CultureInfo

My code:
dateObject.Value.ToString(Model.Culture)
dateObject is of type DateTime? while Model.Culture is of type CultureInfo.
The (culture dependent) output:
17/08/1960 00:00:00
I'd like to remove the 00:00:00 part without having to specify any format provider.
Model.Culture should contains the format for the date already while somewhere else (but where and how?) I'd like to specify not to output any time.
I was thinking to cast DateTime over a Date object but, unfortunately, there is no such object in C#.
Hardcoding the date format directly will result in the impossibility to create a dynamic and culture dependent program.

" without having to specify any format provider"
...
"Hardcoding the date format directly will result in the impossibility to create a dynamic and culture dependent program."
You can use the overload that enables to provide a format string and the culture:
string result = dateObject.Value.ToString("d", Model.Culture);
or you change the culture if that is desired/possible:
System.Threading.Thread.CurrentThread.CurrentCulture = Model.Culture;
string result = dateObject.Value.ToShortDateString();

Maybe you are looking for this:
dateObject.Value.ToString("d", Model.Culture)

Use ToShortDateString it uses the current thread culture.
DateTime dateObject = DateTime.Now;
string s = dateObject.ToShortDateString();

Try the following using string formatting
dateObject.ToString("dd/MM/yyyy");
DATE FORMATS

Unable to parse date time in C#

I know such questions are in ton here. Please go through once
I have a string coming from textbox having current date e.g. 10/9/2012, my class property is of DateTime? type. I am using Convert.ToDateTime(datetime_string_from_textbox) but it gives me a FormatException. I then tried DateTime.ParseExact(string, format, CultureInfo, DateTimeStyle) as suggested by Jon Skeet here but still it gave me the same exception.
One more thing — my local machine date time format is dd-mm-yyyy. When I switch this to mm/dd/yyyy format the code works fine. So basically , I want to know how to parse a valid datetime string to a DateTime object irrespective of the regional settings, or any settings or any dependency on local machine.
Is this possible?
Update : Code in use
employee.JoiningDate = DateTime.ParseExact(string.Format("{0} 00:00:00", JoiningDate.Text.Trim()), "MM/dd/yyyy hh:mm:ss", CultureInfo.InvariantCulture, DateTimeStyles.AdjustToUniversal | DateTimeStyles.AssumeUniversal);
Existing Problem and Required Solution
My system datetime shows 24-10-2012 (that is, 24th Oct) and I have 10/17/2012 in my text box (that is, 17th Oct) since the text box date is also valid and after deployment again the client datetime format will become unknown so, I want a generic way to parse any valid datetime string irrespective of regional settings. Is this possible?

This should work:
var date = DateTime.ParseExact(str, "M/d/yyyy", CultureInfo.InvariantCulture);
As tested bellow: 

Try formatting your date to international date format using this method:
How would you format DateTime in international format?
Also you can check this for your current culture:
Set Default DateTime Format c#

It totally depends on the machine settings. DateTime.ParseExact(str, "dd/MM/yyyy", CultureInfo.InvariantCulture); will work for British format but it will give format exception on US format. So use format according to your machine settings.

Try the following if it works
var formatInfo = new DateTimeFormatInfo();
formatInfo.ShortDatePattern = "MM/dd/yyyy";
DateTime.Parse(date, formatInfo);

DateTime.Parse, Latvian culture settings

I am sending in a string in dd/MM/yyyy format, which is then being parsed into lv-LV culture as set per the web.config globalization setting.
I am then comparing the date to DateTime.Now to see if it is in the past.
The problem is, DateTime.Parse converts my string to dd.MM.yyyy format, but DateTime.Now has MM.dd.yyyy format, so the comparison always fails.
Why would DateTime.Now be different to the output from DateTime.Parse, on the same thread culture?
Thanks!
(Update) This is the code I am using:
InputText contains input from a form in DD.MM.YYYY format
DateTime date = DateTime.Parse(InputText, CultureInfo.CurrentCulture);
// Check it's not in the past
this.IsValid = (date.CompareTo(DateTime.Now) > 0);
[DateTime.Now] in this context is in MM.DD.YYYY format using lv-LV cultureInfo
[date] is in DD.MM.YYYY format after the DateTime.Parse

A DateTime does not have formatting - it is simply a point in time.
If you are viewing it, that means you are outputting it. Use the correct culture to output the date.
DateTime.ToString has overloads that take a format provider such as a CultureInfo:
string formatted = DateTime.ToString(new CultureInfo("lv-LV"));
If not specified (in code or configuration), the default system culture will be used (or CultureInfo.InvariantCulture, in some cases).

If you just want to compare the 2 dates, you don't need to convert to string first.
DateTime myDate = DateTime.Parse(myDateAsString);//with the correct locale to ensure it's correctly parsed
if (myDate < DateTime.Now)
{
//it's in the past
}